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2002
11:
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113
S.
Ct.
2786
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113
S.
Ct.
2786
Page
2
125
L.
Ed.
2d
469,
61
USLW
4805,
27
U.
S.
P.
Q.
2d
1200,
23
Envtl.
L.
Rep.
20,979,
37
Fed.
R.
Evid.
Serv.
1,
Prod.
Liab.
Rep.
(
CCH)
P
13,494
(
Cite
as:
509
U.
S.
579,
113
S.
Ct.
2786)

Copr.
©
West
2002
No
Claim
to
Orig.
U.
S.
Govt.
Works
Supreme
Court
of
the
United
States
William
DAUBERT,
et
ux.,
etc.,
et
al.,
Petitioners,
v.
MERRELL
DOW
PHARMACEUTICALS,
INC.

No.
92­
102.

Argued
March
30,
1993
Decided
June
28,
1993.

Infants
and
their
guardians
ad
litem
sued
pharmaceutical
company
to
recover
for
limb
reduction
birth
defects
allegedly
sustained
as
result
of
mothers'
ingestion
of
antinausea
drug
Bendectin.
The
United
States
District
Court
for
the
Southern
District
of
California,
727
F.
Supp.
570,
granted
company's
motion
for
summary
judgment,
and
plaintiffs
appealed.
The
Court
of
Appeals,
951
F.
2d
1128,
affirmed.
Plaintiffs
filed
petition
for
writ
of
certiorari,
which
was
granted.
The
Supreme
Court,
Justice
Blackmun,
held
that:
(
1)
"
general
acceptance"
is
not
necessary
precondition
to
admissibility
of
scientific
evidence
under
Federal
Rules
of
Evidence,
and
(
2)
Rules
assign
to
trial
judge
the
task
of
ensuring
that
expert's
testimony
both
rests
on
reliable
foundation
and
is
relevant
to
task
at
hand.

Vacated
and
remanded.

Chief
Justice
Rehnquist
filed
opinion
concurring
in
part
and
dissenting
in
part
in
which
Justice
Stevens
joined.

West
Headnotes
[
1]
Evidence
150
157k150
Most
Cited
Cases
Federal
Rules
of
Evidence
superseded
Frye
"
general
acceptance"
test
for
admissibility
of
scientific
evidence.
Fed.
Rules
Evid.
Rule
702,
28
U.
S.
C.
A.

[
2]
Federal
Civil
Procedure
21
170Ak21
Most
Cited
Cases
Supreme
Court
interprets
legislatively
enacted
Federal
Rules
of
Evidence
as
it
would
any
statute.

[
3]
Evidence
99
157k99
Most
Cited
Cases
Basic
standard
of
relevance
under
Federal
Rules
of
Evidence
is
liberal
one.
Fed.
Rules
Evid.
Rules
401,
402,
28
U.
S.
C.
A.
113
S.
Ct.
2786
Page
3
125
L.
Ed.
2d
469,
61
USLW
4805,
27
U.
S.
P.
Q.
2d
1200,
23
Envtl.
L.
Rep.
20,979,
37
Fed.
R.
Evid.
Serv.
1,
Prod.
Liab.
Rep.
(
CCH)
P
13,494
(
Cite
as:
509
U.
S.
579,
113
S.
Ct.
2786)

Copr.
©
West
2002
No
Claim
to
Orig.
U.
S.
Govt.
Works
[
4]
Evidence
150
157k150
Most
Cited
Cases
Rigid
"
general
acceptance"
requirement
for
admission
of
scientific
evidence
would
be
at
odds
with
"
liberal
thrust"
of
Federal
Rules
of
Evidence
and
their
general
approach
of
relaxing
traditional
barriers
to
"
opinion"
testimony.
Fed.
Rules
Evid.
Rule
702,
28
U.
S.
C.
A.

[
5]
Evidence
150
157k150
Most
Cited
Cases
Trial
judge
is
not
disabled
under
Federal
Rules
of
Evidence
from
screening
purportedly
scientific
evidence.
Fed.
Rules
Evid.
Rule
702,
28
U.
S.
C.
A.

[
6]
Evidence
150
157k150
Most
Cited
Cases
Under
Federal
Rules
of
Evidence,
trial
judge
must
ensure
that
any
and
all
scientific
testimony
or
evidence
admitted
is
not
only
relevant,
but
reliable.
Fed.
Rules
Evid.
Rule
702,
28
U.
S.
C.
A.

[
7]
Evidence
150
157k150
Most
Cited
Cases
"
Scientific,"
within
meaning
of
Federal
Rule
of
Evidence
stating
that
if
"
scientific,"
technical,
or
other
specialized
knowledge
will
assist
trier
of
fact
to
understand
evidence
or
to
determine
fact
in
issue
an
expert
may
testify
thereto,
implies
grounding
in
methods
and
procedures
of
science.
Fed.
Rules
Evid.
Rule
702,
28
U.
S.
C.
A.

[
8]
Evidence
508
157k508
Most
Cited
Cases
"
Knowledge,"
within
meaning
of
Federal
Rule
of
Evidence
stating
that
if
scientific,
technical,
or
other
specialized
"
knowledge"
will
assist
trier
of
fact
to
understand
evidence
or
to
determine
fact
in
issue
an
expert
may
testify
thereto,
connotes
more
than
subjective
belief
or
unsupported
speculation.
Fed.
Rules
Evid.
Rule
702,
28
U.
S.
C.
A.

[
9]
Evidence
508
157k508
Most
Cited
Cases
Subject
of
scientific
knowledge
need
not
be
"
known"
to
certainty
to
permit
expert
testimony,
since,
arguably,
there
are
not
certainties
in
science.
Fed.
Rules
Evid.
Rule
702,
28
U.
S.
C.
A.

[
10]
Evidence
508
157k508
Most
Cited
Cases
Inference
or
assertion
must
be
derived
by
scientific
method
to
qualify
as
113
S.
Ct.
2786
Page
4
125
L.
Ed.
2d
469,
61
USLW
4805,
27
U.
S.
P.
Q.
2d
1200,
23
Envtl.
L.
Rep.
20,979,
37
Fed.
R.
Evid.
Serv.
1,
Prod.
Liab.
Rep.
(
CCH)
P
13,494
(
Cite
as:
509
U.
S.
579,
113
S.
Ct.
2786)

Copr.
©
West
2002
No
Claim
to
Orig.
U.
S.
Govt.
Works
"
scientific
knowledge,"
within
meaning
of
Federal
Rule
of
Evidence
stating
that
if
scientific,
technical,
or
other
specialized
knowledge
will
assist
trier
of
fact
to
understand
evidence
or
to
determine
fact
in
issue
an
expert
may
testify
thereto.
Fed.
Rules
Evid.
Rule
702,
28
U.
S.
C.
A.

[
11]
Evidence
555.1
157k555.1
Most
Cited
Cases
For
scientific
testimony
to
be
admitted,
proposed
testimony
must
be
supported
by
appropriate
validation,
in
other
words,
"
good
grounds"
based
on
what
is
known.
Fed.
Rules
Evid.
Rule
702,
28
U.
S.
C.
A.

[
12]
Evidence
508
157k508
Most
Cited
Cases
Requirement
under
Federal
Rule
of
Evidence
that
expert's
testimony
pertain
to
"
scientific
knowledge"
establishes
standard
of
evidentiary
reliability.
Fed.
Rules
Evid.
Rule
702,
28
U.
S.
C.
A.

[
13]
Evidence
150
157k150
Most
Cited
Cases
In
case
involving
scientific
evidence,
evidentiary
reliability
will
be
based
upon
scientific
reliability.
Fed.
Rules
Evid.
Rule
702,
28
U.
S.
C.
A.

[
14]
Evidence
150
157k150
Most
Cited
Cases
Condition
for
admission
of
scientific
evidence
or
testimony
under
Federal
Rule
of
Evidence,
that
evidence
or
testimony
assist
trier
of
fact
to
understand
evidence
or
to
determine
fact
in
issue,
goes
primarily
to
relevance.
Fed.
Rules
Evid.
Rule
702,
28
U.
S.
C.
A.

[
15]
Evidence
150
157k150
Most
Cited
Cases
In
determining
admissibility
of
scientific
evidence
or
testimony,
scientific
validity
for
one
purpose
is
not
necessarily
scientific
validity
for
other,
unrelated
purposes.
Fed.
Rules
Evid.
Rule
702,
28
U.
S.
C.
A.

[
16]
Evidence
150
157k150
Most
Cited
Cases
"
Helpfulness"
standard
under
Federal
Rule
of
Evidence
for
admissibility
of
scientific
evidence
or
testimony
requires
valid
scientific
connection
to
pertinent
inquiry
as
precondition
to
admissibility.
Fed.
Rules
Evid.
Rule
702,
28
U.
S.
C.
A.

[
17]
Evidence
505
157k505
Most
Cited
Cases
113
S.
Ct.
2786
Page
5
125
L.
Ed.
2d
469,
61
USLW
4805,
27
U.
S.
P.
Q.
2d
1200,
23
Envtl.
L.
Rep.
20,979,
37
Fed.
R.
Evid.
Serv.
1,
Prod.
Liab.
Rep.
(
CCH)
P
13,494
(
Cite
as:
509
U.
S.
579,
113
S.
Ct.
2786)

Copr.
©
West
2002
No
Claim
to
Orig.
U.
S.
Govt.
Works
Unlike
ordinary
witness,
expert
is
permitted
wide
latitude
to
offer
opinions,
including
those
that
are
not
based
on
first­
hand
knowledge
or
observation.
Fed.
Rules
Evid.
Rules
701­
703,
28
U.
S.
C.
A.

[
18]
Evidence
508
157k508
Most
Cited
Cases
Presumably,
relaxation
under
Federal
Rules
of
Evidence
of
usual
requirement
of
first­
hand
knowledge
when
there
is
testimony
by
expert
is
premised
on
assumption
that
expert's
opinion
will
have
reliable
basis
in
knowledge
and
experience
of
his
discipline.
Fed.
Rules
Evid.
Rules
701­
703,
28
U.
S.
C.
A.

[
19]
Evidence
508
157k508
Most
Cited
Cases
Faced
with
proffer
of
expert
scientific
testimony,
trial
judge
must
determine
at
outset
whether
expert
is
proposing
to
testify
to
(
1)
scientific
knowledge
that
(
2)
will
assist
trier
of
fact
to
understand
or
determine
fact
in
issue;
preliminary
assessment
must
be
made
of
whether
reasoning
or
methodology
underlying
testimony
is
scientifically
valid
and
of
whether
that
reasoning
or
methodology
properly
can
be
applied
to
facts
in
issue.
Fed.
Rules
Evid.
Rules
104(
a),
702,
28
U.
S.
C.
A.

[
20]
Evidence
546
157k546
Most
Cited
Cases
Preliminary
questions
concerning
qualification
of
person
to
be
witness,
existence
of
privilege,
or
admissibility
of
evidence
should
be
established
by
preponderance
of
proof.
Fed.
Rules
Evid.
Rules
104(
a),
702,
28
U.
S.
C.
A.

[
21]
Evidence
150
157k150
Most
Cited
Cases
Requirements
for
admissibility
of
scientific
testimony
or
opinion
under
Federal
Rule
of
Evidence
do
not
apply
specially
or
exclusively
to
unconventional
evidence.
Fed.
Rules
Evid.
Rule
702,
28
U.
S.
C.
A.

[
22]
Evidence
9
157k9
Most
Cited
Cases
Scientific
theories
that
are
so
firmly
established
as
to
have
obtained
status
of
scientific
law,
such
as
laws
of
thermodynamics,
properly
are
subject
to
judicial
notice.
Fed.
Rules
Evid.
Rule
201,
28
U.
S.
C.
A.

[
23]
Evidence
555.1
157k555.1
Most
Cited
Cases
Definitive
checklist
or
test
does
not
exist
in
making
preliminary
assessment
of
whether
reasoning
or
methodology
underlying
expert
testimony
is
scientifically
valid
and
whether
that
reasoning
or
methodology
properly
can
be
applied
to
facts
in
issue.
Fed.
Rules
Evid.
Rule
104(
a),
28
U.
S.
C.
A.
113
S.
Ct.
2786
Page
6
125
L.
Ed.
2d
469,
61
USLW
4805,
27
U.
S.
P.
Q.
2d
1200,
23
Envtl.
L.
Rep.
20,979,
37
Fed.
R.
Evid.
Serv.
1,
Prod.
Liab.
Rep.
(
CCH)
P
13,494
(
Cite
as:
509
U.
S.
579,
113
S.
Ct.
2786)

Copr.
©
West
2002
No
Claim
to
Orig.
U.
S.
Govt.
Works
[
24]
Evidence
508
157k508
Most
Cited
Cases
Ordinarily,
key
question
to
be
answered
in
determining
whether
theory
or
technique
is
scientific
knowledge
that
will
assist
trier
of
fact,
and,
thus,
whether
expert
testimony
is
admissible,
will
be
whether
theory
or
technique
can
be,
and
has
been,
tested.
Fed.
Rules
Evid.
Rules
104(
a),
702,
28
U.
S.
C.
A.

[
25]
Evidence
508
157k508
Most
Cited
Cases
in
In
determining
whether
theory
or
technique
is
scientific
knowledge
that
will
assist
trier
of
fact,
and,
thus,
whether
expert
testimony
is
admissible,
is
whether
theory
or
technique
has
been
subjected
to
peer
review
and
publication.
Fed.
Rules
Evid.
Rules
104(
a),
702,
28
U.
S.
C.
A.

[
26]
Evidence
508
157k508
Most
Cited
Cases
Publication
of
theory
or
technique,
which
is
but
one
element
of
peer
review,
is
not
sine
qua
non
of
admissibility
of
expert
testimony;
publication
does
not
necessarily
correlate
with
reliability,
and,
in
some
instances,
well­
grounded
but
innovative
theories
will
not
have
been
published.
Fed.
Rules
Evid.
Rules
104(
a),
702,
28
U.
S.
C.
A.

[
27]
Evidence
508
157k508
Most
Cited
Cases
Fact
of
publication
of
theory
or
technique,
or
lack
thereof,
in
peer­
review
journal
will
be
relevant,
though
not
dispositive,
consideration
in
assessing
scientific
validity
of
particular
technique
or
methodology
on
which
expert
opinion
is
premised;
submission
to
scrutiny
of
scientific
community
is
component
of
"
good
science,"
in
part
because
it
increases
likelihood
that
substantive
flaws
in
methodology
will
be
detected.
Fed.
Rules
Evid.
Rules
104(
a),
702,
28
U.
S.
C.
A.

[
28]
Evidence
508
157k508
Most
Cited
Cases
In
determining
admissibility
of
expert
opinion
regarding
particular
scientific
technique,
court
ordinarily
should
consider
known
or
potential
rate
of
error,
and
existence
and
maintenance
of
standards
controlling
technique's
operation.
Fed.
Rules
Evid.
Rules
104(
a),
702,
28
U.
S.
C.
A.

[
29]
Evidence
508
157k508
Most
Cited
Cases
"
General
acceptance"
of
scientific
theory
or
technique
can
have
bearing
in
determining
admissibility
of
expert
testimony.
Fed.
Rules
Evid.
Rules
104(
a),
702,
28
U.
S.
C.
A.
113
S.
Ct.
2786
Page
7
125
L.
Ed.
2d
469,
61
USLW
4805,
27
U.
S.
P.
Q.
2d
1200,
23
Envtl.
L.
Rep.
20,979,
37
Fed.
R.
Evid.
Serv.
1,
Prod.
Liab.
Rep.
(
CCH)
P
13,494
(
Cite
as:
509
U.
S.
579,
113
S.
Ct.
2786)

Copr.
©
West
2002
No
Claim
to
Orig.
U.
S.
Govt.
Works
[
30]
Evidence
150
157k150
Most
Cited
Cases
Widespread
acceptance
of
scientific
theory
or
technique
can
be
important
factor
in
ruling
particular
evidence
admissible,
and
known
technique
that
has
been
able
to
draw
only
minimal
support
within
community
may
properly
be
viewed
with
skepticism.
Fed.
Rules
Evid.
Rules
104(
a),
702,
28
U.
S.
C.
A.

[
31]
Evidence
150
157k150
Most
Cited
Cases
Inquiry
envisioned
by
Federal
Rule
of
Evidence
pertaining
to
admission
of
scientific
testimony
and
evidence
is
flexible
one.
Fed.
Rules
Evid.
Rule
702,
28
U.
S.
C.
A.

[
32]
Evidence
150
157k150
Most
Cited
Cases
Overarching
subject
of
Federal
Rule
of
Evidence
on
admission
of
scientific
testimony
and
evidence
is
scientific
validity,
and,
thus,
evidentiary
relevance
and
reliability,
of
principles
that
underlie
proposed
submission.
Fed.
Rules
Evid.
Rule
702,
28
U.
S.
C.
A.

[
33]
Evidence
150
157k150
Most
Cited
Cases
Focus
of
Federal
Rule
of
Evidence
on
admission
of
scientific
testimony
and
evidence
must
be
solely
on
principles
and
methodology,
not
on
conclusions
that
they
generate.
Fed.
Rules
Evid.
Rule
702,
28
U.
S.
C.
A.

[
34]
Evidence
546
157k546
Most
Cited
Cases
Judge
assessing
proffer
of
expert's
scientific
testimony
under
Federal
Rule
of
Evidence
on
testimony
by
experts
should
also
be
mindful
of
other
applicable
rules,
including
rule
on
expert
opinions
based
on
otherwise
inadmissible
hearsay,
rule
allowing
court
to
procure
assistance
of
expert
of
its
own
choosing,
and
rule
permitting
exclusion
of
relevant
evidence
if
its
probative
value
is
substantially
outweighed
by
danger
of
unfair
prejudice,
confusion
of
issues,
or
misleading
jury.
Fed.
Rules
Evid.
Rules
403,
702,
703,
706,
28
U.
S.
C.
A.

[
35]
Federal
Civil
Procedure
2146
170Ak2146
Most
Cited
Cases
[
35]
Federal
Civil
Procedure
2546
170Ak2546
Most
Cited
Cases
In
event
that
trial
court
concludes
that
scintilla
of
scientific
evidence
presented
supporting
a
position
is
insufficient
to
allow
reasonable
juror
to
conclude
that
position
more
likely
than
not
is
true,
court
remains
free
to
direct
verdict,
and
likewise
to
grant
summary
judgment.
Fed.
Rules
Civ.
Proc.
Rules
50(
a),
56,
28
113
S.
Ct.
2786
Page
8
125
L.
Ed.
2d
469,
61
USLW
4805,
27
U.
S.
P.
Q.
2d
1200,
23
Envtl.
L.
Rep.
20,979,
37
Fed.
R.
Evid.
Serv.
1,
Prod.
Liab.
Rep.
(
CCH)
P
13,494
(
Cite
as:
509
U.
S.
579,
113
S.
Ct.
2786)

Copr.
©
West
2002
No
Claim
to
Orig.
U.
S.
Govt.
Works
U.
S.
C.
A.;
Fed.
Rules
Evid.
Rule
702,
28
U.
S.
C.
A.

[
36]
Federal
Civil
Procedure
21
170Ak21
Most
Cited
Cases
Federal
Rules
of
Evidence
are
designed
not
for
exhaustive
search
for
cosmic
understanding
but
for
particularized
resolution
of
legal
disputes.
**
2789
Syllabus
[
FN*]

FN*
The
syllabus
constitutes
no
part
of
the
opinion
of
the
Court
but
has
been
prepared
by
the
Reporter
of
Decisions
for
the
convenience
of
the
reader.
See
United
States
v.
Detroit
Lumber
Co.,
200
U.
S.
321,
337,
26
S.
Ct.
282,
287,
50
L.
Ed.
499.

*
579
Petitioners,
two
minor
children
and
their
parents,
alleged
in
their
suit
against
respondent
that
the
children's
serious
birth
defects
had
been
caused
by
the
mothers'
prenatal
ingestion
of
Bendectin,
a
prescription
drug
marketed
by
respondent.
The
District
Court
granted
respondent
summary
judgment
based
on
a
well­
credentialed
expert's
affidavit
concluding,
upon
reviewing
the
extensive
published
scientific
literature
on
the
subject,
that
maternal
use
of
Bendectin
has
not
been
shown
to
be
a
risk
factor
for
human
birth
defects.
Although
petitioners
had
responded
with
the
testimony
of
eight
other
well­
credentialed
experts,
who
based
their
conclusion
**
2790
that
Bendectin
can
cause
birth
defects
on
animal
studies,
chemical
structure
analyses,
and
the
unpublished
"
reanalysis"
of
previously
published
human
statistical
studies,
the
court
determined
that
this
evidence
did
not
meet
the
applicable
"
general
acceptance"
standard
for
the
admission
of
expert
testimony.
The
Court
of
Appeals
agreed
and
affirmed,
citing
Frye
v.
United
States,
54
App.
D.
C.
46,
47,
293
F.
1013,
1014,
for
the
rule
that
expert
opinion
based
on
a
scientific
technique
is
inadmissible
unless
the
technique
is
"
generally
accepted"
as
reliable
in
the
relevant
scientific
community.

Held:
The
Federal
Rules
of
Evidence,
not
Frye,
provide
the
standard
for
admitting
expert
scientific
testimony
in
a
federal
trial.
Pp.
2792­
99.

(
a)
Frye's
"
general
acceptance"
test
was
superseded
by
the
Rules'
adoption.
The
Rules
occupy
the
field,
United
States
v.
Abel,
469
U.
S.
45,
49,
105
S.
Ct.
465,
467,
83
L.
Ed.
2d
450,
and,
although
the
common
law
of
evidence
may
serve
as
an
aid
to
their
application,
id.,
at
51­
52,
105
S.
Ct.,
at
468­
469,
respondent's
assertion
that
they
somehow
assimilated
Frye
is
unconvincing.
Nothing
in
the
Rules
as
a
whole
or
in
the
text
and
drafting
history
of
Rule
702,
which
specifically
governs
expert
testimony,
gives
any
indication
that
"
general
acceptance"
is
a
necessary
precondition
to
the
admissibility
of
scientific
evidence.
Moreover,
such
a
rigid
standard
would
be
at
odds
with
the
Rules'
liberal
thrust
and
their
general
approach
of
relaxing
the
traditional
barriers
to
"
opinion"
testimony.
Pp.
2792­
94.

(
b)
The
Rules­­
especially
Rule
702­­
place
appropriate
limits
on
the
admissibility
of
purportedly
scientific
evidence
by
assigning
to
the
trial
*
580
judge
the
task
of
ensuring
that
an
expert's
testimony
both
rests
on
a
reliable
foundation
and
is
relevant
to
the
task
at
hand.
The
reliability
standard
is
established
by
Rule
702'
s
requirement
that
an
expert's
testimony
pertain
to
"
scientific
...
knowledge,"
since
the
adjective
"
scientific"
implies
a
grounding
in
science's
methods
and
procedures,
while
the
word
"
knowledge"
connotes
a
body
of
known
facts
or
of
ideas
inferred
from
such
facts
or
accepted
as
true
on
good
grounds.
The
Rule's
requirement
that
the
testimony
"
assist
the
trier
of
fact
to
understand
the
evidence
or
to
determine
a
fact
in
issue"
goes
primarily
to
relevance
by
demanding
a
valid
scientific
connection
to
the
pertinent
inquiry
as
a
precondition
to
admissibility.
Pp.
2794­
96.

(
c)
Faced
with
a
proffer
of
expert
scientific
testimony
under
Rule
702,
the
trial
113
S.
Ct.
2786
Page
9
125
L.
Ed.
2d
469,
61
USLW
4805,
27
U.
S.
P.
Q.
2d
1200,
23
Envtl.
L.
Rep.
20,979,
37
Fed.
R.
Evid.
Serv.
1,
Prod.
Liab.
Rep.
(
CCH)
P
13,494
(
Cite
as:
509
U.
S.
579,
113
S.
Ct.
2786)

Copr.
©
West
2002
No
Claim
to
Orig.
U.
S.
Govt.
Works
judge,
pursuant
to
Rule
104(
a),
must
make
a
preliminary
assessment
of
whether
the
testimony's
underlying
reasoning
or
methodology
is
scientifically
valid
and
properly
can
be
applied
to
the
facts
at
issue.
Many
considerations
will
bear
on
the
inquiry,
including
whether
the
theory
or
technique
in
question
can
be
(
and
has
been)
tested,
whether
it
has
been
subjected
to
peer
review
and
publication,
its
known
or
potential
error
rate
and
the
existence
and
maintenance
of
standards
controlling
its
operation,
and
whether
it
has
attracted
widespread
acceptance
within
a
relevant
scientific
community.
The
inquiry
is
a
flexible
one,
and
its
focus
must
be
solely
on
principles
and
methodology,
not
on
the
conclusions
that
they
generate.
Throughout,
the
judge
should
also
be
mindful
of
other
applicable
Rules.
Pp.
2796­
98.

(
d)
Cross­
examination,
presentation
of
contrary
evidence,
and
careful
instruction
on
the
burden
of
proof,
rather
than
wholesale
exclusion
under
an
uncompromising
"
general
acceptance"
standard,
is
the
appropriate
means
by
which
evidence
based
on
valid
principles
may
be
challenged.
That
even
limited
screening
by
the
trial
judge,
on
occasion,
will
prevent
the
jury
from
hearing
of
authentic
scientific
breakthroughs
is
simply
a
consequence
of
the
fact
that
the
Rules
are
not
designed
to
seek
cosmic
understanding
but,
rather,
to
resolve
legal
disputes.
Pp.
2798­
99.

951
F.
2d
1128
(
CA9
1991),
vacated
and
remanded.

**
2791
BLACKMUN,
J.,
delivered
the
opinion
for
a
unanimous
Court
with
respect
to
Parts
I
and
II­
A,
and
the
opinion
of
the
Court
with
respect
to
Parts
II­
B,
II­
C,
III,
and
IV,
in
which
WHITE,
O'CONNOR,
SCALIA,
KENNEDY,
SOUTER,
and
THOMAS,
JJ.,
joined.
REHNQUIST,
C.
J.,
filed
an
opinion
concurring
in
part
and
dissenting
in
part,
in
which
STEVENS,
J.,
joined,
post,
p.
­­­­.

*
581
Michael
H.
Gottesman,
Washington,
DC,
for
petitioners.

Charles
Fried,
Cambridge,
MA,
for
respondent.

*
582
Justice
BLACKMUN
delivered
the
opinion
of
the
Court.

In
this
case
we
are
called
upon
to
determine
the
standard
for
admitting
expert
scientific
testimony
in
a
federal
trial.

I
Petitioners
Jason
Daubert
and
Eric
Schuller
are
minor
children
born
with
serious
birth
defects.
They
and
their
parents
sued
respondent
in
California
state
court,
alleging
that
the
birth
defects
had
been
caused
by
the
mothers'
ingestion
of
Bendectin,
a
prescription
antinausea
drug
marketed
by
respondent.
Respondent
removed
the
suits
to
federal
court
on
diversity
grounds.

After
extensive
discovery,
respondent
moved
for
summary
judgment,
contending
that
Bendectin
does
not
cause
birth
defects
in
humans
and
that
petitioners
would
be
unable
to
come
forward
with
any
admissible
evidence
that
it
does.
In
support
of
its
motion,
respondent
submitted
an
affidavit
of
Steven
H.
Lamm,
physician
and
epidemiologist,
who
is
a
well­
credentialed
expert
on
the
risks
from
exposure
to
various
chemical
substances.
[
FN1]
Doctor
Lamm
stated
that
he
had
reviewed
all
the
literature
on
Bendectin
and
human
birth
defects­­
more
than
30
published
studies
involving
over
130,000
patients.
No
study
had
found
Bendectin
to
be
a
human
teratogen
(
i.
e.,
a
substance
capable
of
causing
malformations
in
fetuses).
On
the
basis
of
this
review,
Doctor
Lamm
concluded
that
maternal
use
of
Bendectin
during
the
first
trimester
of
pregnancy
has
not
been
shown
to
be
a
risk
factor
for
human
birth
defects.

FN1.
Doctor
Lamm
received
his
master's
and
doctor
of
medicine
degrees
from
the
113
S.
Ct.
2786
Page
10
125
L.
Ed.
2d
469,
61
USLW
4805,
27
U.
S.
P.
Q.
2d
1200,
23
Envtl.
L.
Rep.
20,979,
37
Fed.
R.
Evid.
Serv.
1,
Prod.
Liab.
Rep.
(
CCH)
P
13,494
(
Cite
as:
509
U.
S.
579,
113
S.
Ct.
2786)

Copr.
©
West
2002
No
Claim
to
Orig.
U.
S.
Govt.
Works
University
of
Southern
California.
He
has
served
as
a
consultant
in
birthdefect
epidemiology
for
the
National
Center
for
Health
Statistics
and
has
published
numerous
articles
on
the
magnitude
of
risk
from
exposure
to
various
chemical
and
biological
substances.
App.
34­
44.

*
583
Petitioners
did
not
(
and
do
not)
contest
this
characterization
of
the
published
record
regarding
Bendectin.
Instead,
they
responded
to
respondent's
motion
with
the
testimony
of
eight
experts
of
their
own,
each
of
whom
also
possessed
impressive
credentials.
[
FN2]
These
experts
had
concluded
that
Bendectin
can
cause
birth
defects.
Their
conclusions
were
based
upon
"
in
vitro"
(
test
tube)
and
"
in
vivo"
(
live)
animal
studies
that
found
a
link
between
Bendectin
and
malformations;
pharmacological
studies
of
the
chemical
structure
of
Bendectin
that
purported
to
show
similarities
between
the
structure
of
the
drug
and
that
of
other
substances
known
to
cause
birth
defects;
and
the
"
reanalysis"
of
previously
**
2792
published
epidemiological
(
human
statistical)
studies.

FN2.
For
example,
Shanna
Helen
Swan,
who
received
a
master's
degree
in
biostatistics
from
Columbia
University
and
a
doctorate
in
statistics
from
the
University
of
California
at
Berkeley,
is
chief
of
the
section
of
the
California
Department
of
Health
and
Services
that
determines
causes
of
birth
defects
and
has
served
as
a
consultant
to
the
World
Health
Organization,
the
Food
and
Drug
Administration,
and
the
National
Institutes
of
Health.
Id.,
at
113­
114,
131­
132.
Stuart
A.
Newman,
who
received
his
bachelor's
degree
in
chemistry
from
Columbia
University
and
his
master's
and
doctorate
in
chemistry
from
the
University
of
Chicago,
is
a
professor
at
New
York
Medical
College
and
has
spent
over
a
decade
studying
the
effect
of
chemicals
on
limb
development.
Id.,
at
54­
56.
The
credentials
of
the
others
are
similarly
impressive.
See
Id.,
at
61­
66,
73­
80,
148­
153,
187­
192,
and
Attachments
12,
20,
21,
26,
31,
and
32
to
Petitioners'
Opposition
to
Summary
Judgment
in
No.
84­
2013­
G(
I)
(
SD
Cal.).

xxx
The
District
Court
granted
respondent's
motion
for
summary
judgment.
The
court
stated
that
scientific
evidence
is
admissible
only
if
the
principle
upon
which
it
is
based
is
"
'
sufficiently
established
to
have
general
acceptance
in
the
field
to
which
it
belongs.'
"
727
F.
Supp.
570,
572
(
S.
D.
Cal.
1989),
quoting
United
States
v.
Kilgus,
571
F.
2d
508,
510
(
CA9
1978).
The
court
concluded
that
petitioners'
evidence
did
not
meet
this
standard.
Given
the
vast
body
of
epidemiological
data
concerning
Bendectin,
the
court
held,
expert
opinion
which
is
not
based
on
epidemiological
evidence
*
584
is
not
admissible
to
establish
causation.
727
F.
Supp.,
at
575.
Thus,
the
animal­
cell
studies,
live­
animal
studies,
and
chemical­
structure
analyses
on
which
petitioners
had
relied
could
not
raise
by
themselves
a
reasonably
disputable
jury
issue
regarding
causation.
Ibid.
Petitioners'
epidemiological
analyses,
based
as
they
were
on
recalculations
of
data
in
previously
published
studies
that
had
found
no
causal
link
between
the
drug
and
birth
defects,
were
ruled
to
be
inadmissible
because
they
had
not
been
published
or
subjected
to
peer
review.
Ibid.

The
United
States
Court
of
Appeals
for
the
Ninth
Circuit
affirmed.
951
F.
2d
1128
(
1991).
Citing
Frye
v.
United
States,
54
App.
D.
C.
46,
47,
293
F.
1013,
1014
(
1923),
the
court
stated
that
expert
opinion
based
on
a
scientific
technique
is
inadmissible
unless
the
technique
is
"
generally
accepted"
as
reliable
in
the
relevant
scientific
community.
951
F.
2d,
at
1129­
1130.
The
court
declared
that
expert
opinion
based
on
a
methodology
that
diverges
"
significantly
from
the
procedures
accepted
by
recognized
authorities
in
the
field
...
cannot
be
shown
to
be
'
generally
accepted
as
a
reliable
technique.'
"
Id.,
at
1130,
quoting
United
States
v.
Solomon,
753
F.
2d
1522,
1526
(
CA9
1985).

The
court
emphasized
that
other
Courts
of
Appeals
considering
the
risks
of
Bendectin
had
refused
to
admit
reanalyses
of
epidemiological
studies
that
had
been
113
S.
Ct.
2786
Page
11
125
L.
Ed.
2d
469,
61
USLW
4805,
27
U.
S.
P.
Q.
2d
1200,
23
Envtl.
L.
Rep.
20,979,
37
Fed.
R.
Evid.
Serv.
1,
Prod.
Liab.
Rep.
(
CCH)
P
13,494
(
Cite
as:
509
U.
S.
579,
113
S.
Ct.
2786)

Copr.
©
West
2002
No
Claim
to
Orig.
U.
S.
Govt.
Works
neither
published
nor
subjected
to
peer
review.
951
F.
2d,
at
1130­
1131.
Those
courts
had
found
unpublished
reanalyses
"
particularly
problematic
in
light
of
the
massive
weight
of
the
original
published
studies
supporting
[
respondent's]
position,
all
of
which
had
undergone
full
scrutiny
from
the
scientific
community."
Id.,
at
1130.
Contending
that
reanalysis
is
generally
accepted
by
the
scientific
community
only
when
it
is
subjected
to
verification
and
scrutiny
by
others
in
the
field,
the
Court
of
Appeals
rejected
petitioners'
reanalyses
as
"
unpublished,
not
subjected
to
the
normal
peer
review
process
and
generated
solely
for
use
in
litigation."
Id.,
at
1131.
The
*
585
court
concluded
that
petitioners'
evidence
provided
an
insufficient
foundation
to
allow
admission
of
expert
testimony
that
Bendectin
caused
their
injuries
and,
accordingly,
that
petitioners
could
not
satisfy
their
burden
of
proving
causation
at
trial.

We
granted
certiorari,
506
U.
S.
914,
113
S.
Ct.
320,
121
L.
Ed.
2d
240
(
1992),
in
light
of
sharp
divisions
among
the
courts
regarding
the
proper
standard
for
the
admission
of
expert
testimony.
Compare,
e.
g.,
United
States
v.
Shorter,
257
U.
S.
App.
D.
C.
358,
363­
364,
809
F.
2d
54,
59­
60
(
applying
the
"
general
acceptance"
standard),
cert.
denied,
484
U.
S.
817,
108
S.
Ct.
71,
98
L.
Ed.
2d
35
(
1987),
with
DeLuca
v.
Merrell
Dow
Pharmaceuticals,
Inc.,
911
F.
2d
941,
955
(
CA3
1990)
(
rejecting
the
"
general
acceptance"
standard).

II
A
In
the
70
years
since
its
formulation
in
the
Frye
case,
the
"
general
acceptance"
test
has
been
the
dominant
standard
for
determining
the
admissibility
of
novel
scientific
evidence
at
trial.
See
E.
Green
&
C.
Nesson,
Problems,
Cases,
and
Materials
on
Evidence
649
(
1983).
Although
under
increasing
attack
of
late,
the
rule
continues
to
be
followed
by
a
**
2793
majority
of
courts,
including
the
Ninth
Circuit.
[
FN3]

FN3.
For
a
catalog
of
the
many
cases
on
either
side
of
this
controversy,
see
P.
Giannelli
&
E.
Imwinkelried,
Scientific
Evidence
§
1­
5,
pp.
10­
14
(
1986
and
Supp.
1991).

The
Frye
test
has
its
origin
in
a
short
and
citation­
free
1923
decision
concerning
the
admissibility
of
evidence
derived
from
a
systolic
blood
pressure
deception
test,
a
crude
precursor
to
the
polygraph
machine.
In
what
has
become
a
famous
(
perhaps
infamous)
passage,
the
then
Court
of
Appeals
for
the
District
of
Columbia
described
the
device
and
its
operation
and
declared:
"
Just
when
a
scientific
principle
or
discovery
crosses
the
line
between
the
experimental
and
demonstrable
stages
*
586
is
difficult
to
define.
Somewhere
in
this
twilight
zone
the
evidential
force
of
the
principle
must
be
recognized,
and
while
courts
will
go
a
long
way
in
admitting
expert
testimony
deduced
from
a
wellrecognized
scientific
principle
ordiscovery,
the
thing
from
which
the
deduction
is
made
must
be
sufficiently
established
to
have
gained
general
acceptance
in
the
particular
field
in
which
it
belongs."
54
App.
D.
C.,
at
47,
293
F.,
at
1014
(
emphasis
added).
Because
the
deception
test
had
"
not
yet
gained
such
standing
and
scientific
recognition
among
physiological
and
psychological
authorities
as
would
justify
the
courts
in
admitting
expert
testimony
deduced
from
the
discovery,
development,
and
experiments
thus
far
made,"
evidence
of
its
results
was
ruled
inadmissible.
Ibid.

[
1]
The
merits
of
the
Frye
test
have
been
much
debated,
and
scholarship
on
its
proper
scope
and
application
is
legion.
[
FN4]
*
587
Petitioners'
primary
attack,
however,
is
not
on
the
content
but
on
the
continuing
authority
of
the
rule.
They
contend
that
the
Frye
test
was
superseded
by
the
adoption
of
the
Federal
Rules
of
Evidence.
[
FN5]
We
agree.
113
S.
Ct.
2786
Page
12
125
L.
Ed.
2d
469,
61
USLW
4805,
27
U.
S.
P.
Q.
2d
1200,
23
Envtl.
L.
Rep.
20,979,
37
Fed.
R.
Evid.
Serv.
1,
Prod.
Liab.
Rep.
(
CCH)
P
13,494
(
Cite
as:
509
U.
S.
579,
113
S.
Ct.
2786)

Copr.
©
West
2002
No
Claim
to
Orig.
U.
S.
Govt.
Works
FN4.
See,
e.
g.,
Green,
Expert
Witnesses
and
Sufficiency
of
Evidence
in
Toxic
Substances
Litigation:
The
Legacy
of
Agent
Orange
and
Bendectin
Litigation,
86
Nw.
U.
L.
Rev.
643
(
1992)
(
hereinafter
Green);
Becker
&
Orenstein,
The
Federal
Rules
of
Evidence
After
Sixteen
Years­­
the
Effect
of
"
Plain
Meaning"
Jurisprudence,
the
Need
for
an
Advisory
Committee
on
the
Rules
of
Evidence,
and
Suggestions
for
Selective
Revision
of
the
Rules,
60
Geo.
Wash.
L.
Rev.
857,
876­
885
(
1992);
Hanson,
James
Alphonzo
Frye
is
Sixty­
Five
Years
Old;
Should
He
Retire?,"
16
West.
St.
U.
L.
Rev.
357
(
1989);
Black,
A
Unified
Theory
of
Scientific
Evidence,
56
Ford.
L.
Rev.
595
(
1988);
Imwinkelried,
The
"
Bases"
of
Expert
Testimony:
The
Syllogistic
Structure
of
Scientific
Testimony,
67
N.
C.
L.
Rev.
1
(
1988);
Proposals
for
a
Model
Rule
on
the
Admissibility
of
Scientific
Evidence,
26
Jurimetrics
J.
235
(
1986);
Giannelli,
The
Admissibility
of
Novel
Scientific
Evidence:
Frye
v.
United
States,
a
Half­
Century
Later,
80
Colum.
L.
Rev.
1197
(
1980);
The
Supreme
Court,
1986
Term,
101
Harv.
L.
Rev.
7,
119,
125­
127
(
1987).
Indeed,
the
debates
over
Frye
are
such
a
well­
established
part
of
the
academic
landscape
that
a
distinct
term­­"
Frye­
ologist"­­
has
been
advanced
to
describe
those
who
take
part.
See
Behringer,
Introduction,
Proposals
for
a
Model
Rule
on
the
Admissibility
of
Scientific
Evidence,
26
Jurimetrics
J.
237,
239
(
1986),
quoting
Lacey,
Scientific
Evidence,
24
Jurimetrics
J.
254,
264
(
1984).

FN5.
Like
the
question
of
Frye'
s
merit,
the
dispute
over
its
survival
has
divided
courts
and
commentators.
Compare,
e.
g.,
United
States
v.
Williams,
583
F.
2d
1194
(
CA2
1978)
(
Frye
is
superseded
by
the
Rules
of
Evidence),
cert.
denied,
439
U.
S.
1117,
99
S.
Ct.
1025,
59
L.
Ed.
2d
77
(
1979)
with
Christophersen
v.
Allied­
Signal
Corp.,
939
F.
2d
1106,
1111,
1115­
1116
(
CA5
1991)
(
en
banc)
(
Frye
and
the
Rules
coexist),
cert.
denied,
503
U.
S.
912,
112
S.
Ct.
1280,
117
L.
Ed.
2d
506
(
1992),
3
J.
Weinstein
&
M.
Berger,
Weinstein's
Evidence
¶
702[
03],
pp.
702­
36
to
702­
37
(
1988)
(
hereinafter
Weinstein
&
Berger)
(
Frye
is
dead),
and
M.
Graham,
Handbook
of
Federal
Evidence
§
703.2
(
3d
ed.
1991)
(
Frye
lives).
See
generally
P.
Giannelli
&
E.
Imwinkelried,
Scientific
Evidence
§
1­
5,
at
28­
29
(
citing
authorities).

[
2][
3]
We
interpret
the
legislatively
enacted
Federal
Rules
of
Evidence
as
we
would
any
statute.
Beech
Aircraft
Corp.
v.
Rainey,
488
U.
S.
153,
163,
109
S.
Ct.
439,
446,
102
L.
Ed.
2d
445
(
1988).
Rule
402
provides
the
baseline:
"
All
relevant
evidence
is
admissible,
except
as
otherwise
provided
by
the
Constitution
of
the
United
States,
by
Act
of
Congress,
**
2794
by
these
rules,
or
by
other
rules
prescribed
by
the
Supreme
Court
pursuant
to
statutory
authority.
Evidence
which
is
not
relevant
is
not
admissible."
"
Relevant
evidence"
is
defined
as
that
which
has
"
any
tendency
to
make
the
existence
of
any
fact
that
is
of
consequence
to
the
determination
of
the
action
more
probable
or
less
probable
than
it
would
be
without
the
evidence."
Rule
401.
The
Rule's
basic
standard
of
relevance
thus
is
a
liberal
one.

Frye,
of
course,
predated
the
Rules
by
half
a
century.
In
United
States
v.
Abel,
469
U.
S.
45,
105
S.
Ct.
465,
83
L.
Ed.
2d
450
(
1984),
we
considered
the
pertinence
of
background
common
law
in
interpreting
the
Rules
of
Evidence.
We
noted
that
the
Rules
occupy
the
field,
id.,
at
49,
105
S.
Ct.,
at
467,
but,
quoting
Professor
Cleary,
the
Reporter,
*
588
explained
that
the
common
law
nevertheless
could
serve
as
an
aid
to
their
application:
"
'
In
principle,
under
the
Federal
Rules
no
common
law
of
evidence
remains.
"
All
relevant
evidence
is
admissible,
except
as
otherwise
provided...."
In
reality,
of
course,
the
body
of
common
law
knowledge
continues
to
exist,
though
in
the
somewhat
altered
form
of
a
source
of
guidance
in
the
exercise
of
delegated
powers.'
"
Id.,
at
51­
52,
105
S.
Ct.,
at
469.
We
found
the
common­
law
precept
at
issue
in
the
Abel
case
entirely
consistent
with
Rule
402'
s
general
requirement
of
admissibility,
and
considered
it
unlikely
that
the
drafters
had
intended
to
change
the
rule.
Id.,
at
50­
51,
105
S.
Ct.,
at
468­
469.
In
Bourjaily
v.
United
States,
483
U.
S.
171,
107
S.
Ct.
2775,
97
L.
Ed.
2d
144
(
1987),
on
113
S.
Ct.
2786
Page
13
125
L.
Ed.
2d
469,
61
USLW
4805,
27
U.
S.
P.
Q.
2d
1200,
23
Envtl.
L.
Rep.
20,979,
37
Fed.
R.
Evid.
Serv.
1,
Prod.
Liab.
Rep.
(
CCH)
P
13,494
(
Cite
as:
509
U.
S.
579,
113
S.
Ct.
2786)

Copr.
©
West
2002
No
Claim
to
Orig.
U.
S.
Govt.
Works
the
other
hand,
the
Court
was
unable
to
find
a
particular
common­
law
doctrine
in
the
Rules,
and
so
held
it
superseded.

[
4]
Here
there
is
a
specific
Rule
that
speaks
to
the
contested
issue.
Rule
702,
governing
expert
testimony,
provides:
"
If
scientific,
technical,
or
other
specialized
knowledge
will
assist
the
trier
of
fact
to
understand
the
evidence
or
to
determine
a
fact
in
issue,
a
witness
qualified
as
an
expert
by
knowledge,
skill,
experience,
training,
or
education,
may
testify
thereto
in
the
form
of
an
opinion
or
otherwise."
Nothing
in
the
text
of
this
Rule
establishes
"
general
acceptance"
as
an
absolute
prerequisite
to
admissibility.
Nor
does
respondent
present
any
clear
indication
that
Rule
702
or
the
Rules
as
a
whole
were
intended
to
incorporate
a
"
general
acceptance"
standard.
The
drafting
history
makes
no
mention
of
Frye,
and
a
rigid
"
general
acceptance"
requirement
would
be
at
odds
with
the
"
liberal
thrust"
of
the
Federal
Rules
and
their
"
general
approach
of
relaxing
the
traditional
barriers
to
'
opinion'
testimony."
Beech
Aircraft
Corp.
v.
Rainey,
488
U.
S.,
at
169,
109
S.
Ct.,
at
450
(
citing
Rules
701
to
705).
See
also
Weinstein,
Rule
702
of
the
Federal
Rules
of
Evidence
is
*
589
Sound;
It
Should
Not
Be
Amended,
138
F.
R.
D.
631
(
1991)
("
The
Rules
were
designed
to
depend
primarily
upon
lawyer­
adversaries
and
sensible
triers
of
fact
to
evaluate
conflicts").
Given
the
Rules'
permissive
backdrop
and
their
inclusion
of
a
specific
rule
on
expert
testimony
that
does
not
mention
"
'
general
acceptance,'
"
the
assertion
that
the
Rules
somehow
assimilated
Frye
is
unconvincing.
Frye
made
"
general
acceptance"
the
exclusive
test
for
admitting
expert
scientific
testimony.
That
austere
standard,
absent
from,
and
incompatible
with,
the
Federal
Rules
of
Evidence,
should
not
be
applied
in
federal
trials.
[
FN6]

FN6.
Because
we
hold
that
Frye
has
been
superseded
and
base
the
discussion
that
follows
on
the
content
of
the
congressionally
enacted
Federal
Rules
of
Evidence,
we
do
not
address
petitioners'
argument
that
application
of
the
Frye
rule
in
this
diversity
case,
as
the
application
of
a
judge­
made
rule
affecting
substantive
rights,
would
violate
the
doctrine
of
Erie
R.
Co.
v.
Tompkins,
304
U.
S.
64,
58
S.
Ct.
817,
82
L.
Ed.
1188
(
1938).

B
[
5][
6]
That
the
Frye
test
was
displaced
by
the
Rules
of
Evidence
does
not
mean,
**
2795
however,
that
the
Rules
themselves
place
no
limits
on
the
admissibility
of
purportedly
scientific
evidence.
[
FN7]
Nor
is
the
trial
judge
disabled
from
screening
such
evidence.
To
the
contrary,
under
the
Rules
the
trial
judge
must
ensure
that
any
and
all
scientifictestimony
or
evidence
admitted
is
not
only
relevant,
but
reliable.

FN7.
THE
CHIEF
JUSTICE
"
do[
es]
not
doubt
that
Rule
702
confides
to
the
judge
some
gatekeeping
responsibility,"
post,
at
2800,
but
would
neither
say
how
it
does
so
nor
explain
what
that
role
entails.
We
believe
the
better
course
is
to
note
the
nature
and
source
of
the
duty.

[
7][
8][
9][
10][
11][
12][
13]
The
primary
locus
of
this
obligation
is
Rule
702,
which
clearly
contemplates
some
degree
of
regulation
of
the
subjects
and
theories
about
which
an
expert
may
testify.
"
If
scientific,
technical,
or
other
specialized
knowledge
will
assist
the
trier
of
fact
to
understand
the
evidence
or
to
determine
a
fact
in
issue"
an
expert
"
may
testify
thereto."
(
Emphasis
added.)
The
subject
of
an
expert's
testimony
must
*
590
be
"
scientific
...
knowledge."
[
FN8]
The
adjective
"
scientific"
implies
a
grounding
in
the
methods
and
procedures
of
science.
Similarly,
the
word
"
knowledge"
connotes
more
than
subjective
belief
or
unsupported
speculation.
The
term
"
applies
to
any
body
of
known
facts
or
to
any
body
of
ideas
inferred
from
such
facts
or
accepted
as
truths
on
good
grounds."
Webster's
Third
113
S.
Ct.
2786
Page
14
125
L.
Ed.
2d
469,
61
USLW
4805,
27
U.
S.
P.
Q.
2d
1200,
23
Envtl.
L.
Rep.
20,979,
37
Fed.
R.
Evid.
Serv.
1,
Prod.
Liab.
Rep.
(
CCH)
P
13,494
(
Cite
as:
509
U.
S.
579,
113
S.
Ct.
2786)

Copr.
©
West
2002
No
Claim
to
Orig.
U.
S.
Govt.
Works
New
International
Dictionary
1252
(
1986).
Of
course,
it
would
be
unreasonable
to
conclude
that
the
subject
of
scientific
testimony
must
be
"
known"
to
a
certainty;
arguably,
there
are
no
certainties
in
science.
See,
e.
g.,
Brief
for
Nicolaas
Bloembergen
et
al.
as
Amici
Curiae
9
("
Indeed,
scientists
do
not
assert
that
they
know
what
is
immutably
'
true'­­
they
are
committed
to
searching
for
new,
temporary,
theories
to
explain,
as
best
they
can,
phenomena");
Brief
for
American
Association
for
the
Advancement
of
Science
et
al.
as
Amici
Curiae
7­
8
("
Science
is
not
an
encyclopedic
body
of
knowledge
about
the
universe.
Instead,
it
represents
a
process
for
proposing
and
refining
theoretical
explanations
about
the
world
that
are
subject
to
further
testing
and
refinement"
(
emphasis
in
original)).
But,
in
order
to
qualify
as
"
scientific
knowledge,"
an
inference
or
assertion
must
be
derived
by
the
scientific
method.
Proposed
testimony
must
be
supported
by
appropriate
validation­­
i.
e.,
"
good
grounds,"
based
on
what
is
known.
In
short,
the
requirement
that
an
expert's
testimony
pertain
to
"
scientific
knowledge"
establishes
a
standard
of
evidentiary
reliability.
[
FN9]

FN8.
Rule
702
also
applies
to
"
technical,
or
other
specialized
knowledge."
Our
discussion
is
limited
to
the
scientific
context
because
that
is
the
nature
of
the
expertise
offered
here.

FN9.
We
note
that
scientists
typically
distinguish
between
"
validity"
(
does
the
principle
support
what
it
purports
to
show?)
and
"
reliability"
(
does
application
of
the
principle
produce
consistent
results?).
See
Black,
56
Ford.
L.
Rev.,
at
599.
Although
"
the
difference
between
accuracy,
validity,
and
reliability
may
be
such
that
each
is
distinct
from
the
other
by
no
more
than
a
hen's
kick,"
Starrs,
Frye
v.
United
States
Restructured
and
Revitalized:
A
Proposal
to
Amend
Federal
Evidence
Rule
702,
26
Jurimetrics
J.
249,
256
(
1986),
our
reference
here
is
to
evidentiary
reliability­­
that
is,
trustworthiness.
Cf.,
e.
g.,
Advisory
Committee's
Notes
on
Fed.
Rule
Evid.
602,
28
U.
S.
C.
App.,
p.
755
("
'[
T]
he
rule
requiring
that
a
witness
who
testifies
to
a
fact
which
can
be
perceived
by
the
senses
must
have
had
an
opportunity
to
observe,
and
must
have
actually
observed
the
fact'
is
a
'
most
pervasive
manifestation'
of
the
common
law
insistence
upon
'
the
most
reliable
sources
of
information'
"
(
citation
omitted));
Advisory
Committee's
Notes
on
Art.
VIII
of
Rules
of
Evidence,
28
U.
S.
C.
App.,
p.
770
(
hearsay
exceptions
will
be
recognized
only
"
under
circumstances
supposed
to
furnish
guarantees
of
trustworthiness").
In
a
case
involving
scientific
evidence,
evidentiary
reliability
will
be
based
upon
scientific
validity.

[
14][
15][
16]
*
591
Rule
702
further
requires
that
the
evidence
or
testimony
"
assist
the
trier
of
fact
to
understand
the
evidence
or
to
determine
a
fact
in
issue."
This
condition
goes
primarily
to
relevance.
"
Expert
testimony
which
does
not
relate
to
any
issue
in
the
case
is
not
relevant
and,
ergo,
non­
helpful."
3
Weinstein
&
Berger
¶
702[
02],
p.
702­
18.
See
also
United
States
v.
Downing,
753
F.
2d
1224,
1242
(
CA3
1985)
("
An
additional
consideration
**
2796
under
Rule
702­­
and
another
aspect
of
relevancy­­
is
whether
expert
testimony
proffered
in
the
case
is
sufficiently
tied
to
the
facts
of
the
case
that
it
will
aid
the
jury
in
resolving
a
factual
dispute").
The
consideration
has
been
aptly
described
by
Judge
Becker
as
one
of
"
fit."
Ibid.
"
Fit"
is
not
always
obvious,
and
scientific
validity
for
one
purpose
is
not
necessarily
scientific
validity
for
other,
unrelated
purposes.
See
Starrs,
Frye
v.
United
States
Restructured
and
Revitalized:
A
Proposal
to
Amend
Federal
Evidence
Rule
702,
26
Jurimetrics
J.
249,
258
(
1986).
The
study
of
the
phases
of
the
moon,
for
example,
may
provide
valid
scientific
"
knowledge"
about
whether
a
certain
night
was
dark,
and
if
darkness
is
a
fact
in
issue,
the
knowledge
will
assist
the
trier
of
fact.
However
(
absent
creditable
grounds
supporting
such
a
link),
evidence
that
the
moon
was
full
on
a
certain
night
will
not
assist
the
trier
of
fact
in
determining
whether
an
individual
was
unusually
likely
to
have
behaved
irrationally
on
that
night.
Rule
702'
s
"
helpfulness"
*
592
standard
requires
avalid
scientific
connection
to
the
pertinent
inquiry
as
a
precondition
to
admissibility.
113
S.
Ct.
2786
Page
15
125
L.
Ed.
2d
469,
61
USLW
4805,
27
U.
S.
P.
Q.
2d
1200,
23
Envtl.
L.
Rep.
20,979,
37
Fed.
R.
Evid.
Serv.
1,
Prod.
Liab.
Rep.
(
CCH)
P
13,494
(
Cite
as:
509
U.
S.
579,
113
S.
Ct.
2786)

Copr.
©
West
2002
No
Claim
to
Orig.
U.
S.
Govt.
Works
[
17][
18]
That
these
requirements
are
embodied
in
Rule
702
is
not
surprising.
Unlike
an
ordinary
witness,
see
Rule
701,
an
expert
is
permitted
wide
latitude
to
offer
opinions,
including
those
that
are
not
based
on
firsthand
knowledge
or
observation.
See
Rules
702
and
703.
Presumably,
this
relaxation
of
the
usual
requirement
of
firsthand
knowledge­­
a
rule
which
represents
"
a
'
most
pervasive
manifestation'
of
the
common
law
insistence
upon
'
the
most
reliable
sources
of
information,'
"
Advisory
Committee's
Notes
on
Fed.
Rule
Evid.
602,
28
U.
S.
C.
App.,
p.
755
(
citation
omitted)­­
is
premised
on
an
assumption
that
the
expert's
opinion
will
have
a
reliable
basis
in
the
knowledge
and
experience
of
his
discipline.

C
[
19][
20][
21][
22][
23]
Faced
with
a
proffer
of
expert
scientific
testimony,
then,
the
trial
judge
must
determine
at
the
outset,
pursuant
to
Rule
104(
a),
[
FN10]
whether
the
expert
is
proposing
to
testify
to
(
1)
scientific
knowledge
that
(
2)
will
assist
the
trier
of
fact
to
understand
or
determine
a
fact
in
issue.
[
FN11]
This
entails
a
preliminary
assessment
of
whether
the
reasoning
or
methodology
*
593
underlying
the
testimony
is
scientifically
valid
and
of
whether
that
reasoning
or
methodology
properly
can
be
applied
to
the
facts
in
issue.
We
are
confident
that
federal
judges
possess
the
capacity
to
undertake
this
review.
Many
factors
will
bear
on
the
inquiry,
and
we
do
not
presume
to
set
out
a
definitive
checklist
or
test.
But
some
general
observations
are
appropriate.

FN10.
Rule
104(
a)
provides:
"
Preliminary
questions
concerning
the
qualification
of
a
person
to
be
a
witness,
the
existence
of
a
privilege,
or
the
admissibility
of
evidence
shall
be
determined
by
the
court,
subject
to
the
provisions
of
subdivision
(
b)
[
pertaining
to
conditional
admissions].
In
making
its
determination
it
is
not
bound
by
the
rules
of
evidence
except
those
with
respect
to
privileges."
These
matters
should
be
established
by
a
preponderance
of
proof.
See
Bourjaily
v.
United
States,
483
U.
S.
171,
175­
176,
107
S.
Ct.
2775,
2778­
2779,
97
L.
Ed.
2d
144
(
1987).

FN11.
Although
the
Frye
decision
itself
focused
exclusively
on
"
novel"
scientific
techniques,
we
do
not
read
the
requirements
of
Rule
702
to
apply
specially
or
exclusively
to
unconventional
evidence.
Of
course,
wellestablished
propositions
are
less
likely
to
be
challenged
than
those
that
are
novel,
and
they
are
more
handily
defended.
Indeed,
theories
that
are
so
firmly
established
as
to
have
attained
the
status
of
scientific
law,
such
as
the
laws
of
thermodynamics,
properly
are
subject
to
judicial
notice
under
Federal
Rule
of
Evidence
201.

[
24]
Ordinarily,
a
key
question
to
be
answered
in
determining
whether
a
theory
or
technique
is
scientific
knowledge
that
will
assist
the
trier
of
fact
will
be
whether
it
can
be
(
and
has
been)
tested.
"
Scientific
methodology
today
is
based
on
generating
hypotheses
and
testing
them
to
see
if
they
can
be
falsified;
indeed,
this
methodology
is
what
distinguishes
science
from
other
fields
of
human
inquiry."
Green
645.
See
also
C.
Hempel,
Philosophy
of
Natural
Science
49
(
1966)
**
2797
("[
T]
he
statements
constituting
a
scientific
explanation
must
be
capable
of
empirical
test");
K.
Popper,
Conjectures
and
Refutations:
The
Growth
of
Scientific
Knowledge
37
(
5th
ed.
1989)
("[
T]
he
criterion
of
the
scientific
status
of
a
theory
is
its
falsifiability,
or
refutability,
or
testability")
(
emphasis
deleted).

[
25][
26][
27]
Another
pertinent
consideration
is
whether
the
theory
or
technique
has
been
subjected
to
peer
review
and
publication.
Publication
(
which
is
but
one
element
of
peer
review)
is
not
a
sine
qua
non
of
admissibility;
it
does
not
necessarily
correlate
with
reliability,
see
S.
Jasanoff,
The
Fifth
Branch:
Science
Advisors
as
Policymakers
61­
76
(
1990),
and
in
some
instances
well­
grounded
but
113
S.
Ct.
2786
Page
16
125
L.
Ed.
2d
469,
61
USLW
4805,
27
U.
S.
P.
Q.
2d
1200,
23
Envtl.
L.
Rep.
20,979,
37
Fed.
R.
Evid.
Serv.
1,
Prod.
Liab.
Rep.
(
CCH)
P
13,494
(
Cite
as:
509
U.
S.
579,
113
S.
Ct.
2786)

Copr.
©
West
2002
No
Claim
to
Orig.
U.
S.
Govt.
Works
innovative
theories
will
not
have
been
published,
see
Horrobin,
The
Philosophical
Basis
of
Peer
Review
and
the
Suppression
of
Innovation,
263
JAMA
1438
(
1990).
Some
propositions,
moreover,
are
too
particular,
too
new,
or
of
too
limited
interest
to
be
published.
But
submission
to
the
scrutiny
of
the
scientific
community
is
a
component
of
"
good
science,"
in
part
because
it
increases
the
likelihood
that
substantive
flaws
in
methodology
will
be
detected.
See
J.
Ziman,
Reliable
Knowledge:
An
Exploration
*
594
of
the
Grounds
for
Belief
in
Science
130­
133
(
1978);
Relman
&
Angell,
How
Good
Is
Peer
Review?,
321
New
Eng.
J.
Med.
827
(
1989).
The
fact
of
publication
(
or
lack
thereof)
in
a
peer
reviewed
journal
thus
will
be
a
relevant,
though
not
dispositive,
consideration
in
assessing
the
scientific
validity
of
a
particular
technique
or
methodology
on
which
an
opinion
is
premised.

[
28]
Additionally,
in
the
case
of
a
particular
scientific
technique,
the
court
ordinarily
should
consider
the
known
or
potential
rate
of
error,
see,
e.
g.,
United
States
v.
Smith,
869
F.
2d
348,
353­
354
(
CA7
1989)
(
surveying
studies
of
the
error
rate
of
spectrographic
voice
identification
technique),
and
the
existence
and
maintenance
of
standards
controlling
the
technique's
operation,
see
United
States
v.
Williams,
583
F.
2d
1194,
1198
(
CA2
1978)
(
noting
professional
organization's
standard
governing
spectrographic
analysis),
cert.
denied,
439
U.
S.
1117,
99
S.
Ct.
1025,
59
L.
Ed.
2d
77
(
1979).

[
29][
30]
Finally,
"
general
acceptance"
can
yet
have
a
bearing
on
the
inquiry.
A
"
reliability
assessment
does
not
require,
although
it
does
permit,
explicit
identification
of
a
relevant
scientific
community
and
an
express
determination
of
a
particular
degree
of
acceptance
within
that
community."
United
States
v.
Downing,
753
F.
2d,
at
1238.
See
also
3
Weinstein
&
Berger
¶
702[
03],
pp.
702­
41
to
702­
42.
Widespread
acceptance
can
be
an
important
factor
in
ruling
particular
evidence
admissible,
and
"
a
known
technique
which
has
been
able
to
attract
only
minimal
support
within
the
community,"
Downing,
753
F.
2d,
at
1238,
may
properly
be
viewed
with
skepticism.

[
31][
32][
33]
The
inquiry
envisioned
by
Rule
702
is,
we
emphasize,
a
flexible
one.
[
FN12]
Its
overarching
subject
is
the
scientific
validity
*
595
and
thus
the
evidentiary
relevance
and
reliability­­
of
the
principles
that
underlie
a
proposed
submission.
The
focus,
of
course,
must
be
solely
on
principles
and
methodology,
not
on
the
conclusions
that
they
generate.

FN12.
A
number
of
authorities
have
presented
variations
on
the
reliability
approach,
each
with
its
own
slightly
different
set
of
factors.
See,
e.
g.,
Downing,
753
F.
2d,
at
1238­
1239
(
on
which
our
discussion
draws
in
part);
3
Weinstein
&
Berger
¶
702[
03],
pp.
702­
41
to
702­
42
(
on
which
the
Downing
court
in
turn
partially
relied);
McCormick,
Scientific
Evidence:
Defining
a
New
Approach
to
Admissibility,
67
Iowa
L.
Rev.
879,
911­
912
(
1982);
and
Symposium
on
Science
and
the
Rules
of
Evidence,
99
F.
R.
D.
187,
231
(
1983)
(
statement
by
Margaret
Berger).
To
the
extent
that
they
focus
on
the
reliability
of
evidence
as
ensured
by
the
scientific
validity
of
its
underlying
principles,
all
these
versions
may
well
have
merit,
although
we
express
no
opinion
regarding
any
of
their
particular
details.

[
34]
Throughout,
a
judge
assessing
a
proffer
of
expert
scientific
testimony
under
Rule
702
should
also
be
mindful
of
other
applicable
rules.
Rule
703
provides
that
expert
opinions
based
on
otherwise
inadmissible**
2798
hearsay
are
to
be
admitted
only
if
the
facts
or
data
are
"
of
a
type
reasonably
relied
upon
by
experts
in
the
particular
field
in
forming
opinions
or
inferences
upon
the
subject."
Rule
706
allows
the
court
at
its
discretion
to
procure
the
assistance
of
an
expert
of
its
own
choosing.
Finally,
Rule
403
permits
the
exclusion
of
relevant
evidence
"
if
its
probative
value
is
substantially
outweighed
by
the
danger
of
unfair
prejudice,
confusion
of
the
issues,
or
misleading
the
jury...."
Judge
Weinstein
has
explained:
"
Expert
evidence
can
be
both
powerful
and
quite
misleading
because
of
the
difficulty
in
evaluating
it.
Because
of
this
risk,
the
judge
in
weighing
possible
prejudice
113
S.
Ct.
2786
Page
17
125
L.
Ed.
2d
469,
61
USLW
4805,
27
U.
S.
P.
Q.
2d
1200,
23
Envtl.
L.
Rep.
20,979,
37
Fed.
R.
Evid.
Serv.
1,
Prod.
Liab.
Rep.
(
CCH)
P
13,494
(
Cite
as:
509
U.
S.
579,
113
S.
Ct.
2786)

Copr.
©
West
2002
No
Claim
to
Orig.
U.
S.
Govt.
Works
against
probative
force
under
Rule
403
of
the
present
rules
exercises
more
control
over
experts
than
over
lay
witnesses."
Weinstein,
138
F.
R.
D.,
at
632.

III
[
35]
We
conclude
by
briefly
addressing
what
appear
to
be
two
underlying
concerns
of
the
parties
and
amici
in
this
case.
Respondent
expresses
apprehension
that
abandonment
of
"
general
acceptance"
as
the
exclusive
requirement
for
admission
will
result
in
a
"
free­
for­
all"
in
which
befuddled
juries
are
confounded
by
absurd
and
irrational
pseudoscientific
assertions.
*
596
In
this
regard
respondent
seems
to
us
to
be
overly
pessimistic
about
the
capabilities
of
the
jury
and
of
the
adversary
system
generally.
Vigorous
cross­
examination,
presentation
of
contrary
evidence,
and
careful
instruction
on
the
burden
of
proof
are
the
traditional
and
appropriate
means
of
attacking
shaky
but
admissible
evidence.
See
Rock
v.
Arkansas,
483
U.
S.
44,
61,
107
S.
Ct.
2704,
2714,
97
L.
Ed.
2d
37
(
1987).
Additionally,
in
the
event
the
trial
court
concludes
that
the
scintilla
of
evidence
presented
supporting
a
position
is
insufficient
to
allow
a
reasonable
juror
to
conclude
that
the
position
more
likely
than
not
is
true,
the
court
remains
free
to
direct
a
judgment,
Fed.
Rule
Civ.
Proc.
50(
a),
and
likewise
to
grant
summary
judgment,
Fed.
Rule
Civ.
Proc.
56.
Cf.,
e.
g.,
Turpin
v.
Merrell
Dow
Pharmaceuticals,
Inc.,
959
F.
2d
1349
(
CA6)
(
holding
that
scientific
evidence
that
provided
foundation
for
expert
testimony,
viewed
in
the
light
most
favorable
to
plaintiffs,
was
not
sufficient
to
allow
a
jury
to
find
it
more
probable
than
not
that
defendant
caused
plaintiff's
injury),
cert.
denied,
506
U.
S.
826,
113
S.
Ct.
84,
121
L.
Ed.
2d
47
(
1992);
Brock
v.
Merrell
Dow
Pharmaceuticals,
Inc.,
874
F.
2d
307
(
CA5
1989)
(
reversing
judgment
entered
on
jury
verdict
for
plaintiffs
because
evidence
regarding
causation
was
insufficient),
modified,
884
F.
2d
166
(
CA5
1989),
cert.
denied,
494
U.
S.
1046,
110
S.
Ct.
1511,
108
L.
Ed.
2d
646
(
1990);
Green
680­
681.
These
conventional
devices,
rather
than
wholesale
exclusion
under
an
uncompromising
"
general
acceptance"
test,
are
the
appropriate
safeguards
where
the
basis
of
scientific
testimony
meets
the
standards
of
Rule
702.

[
36]
Petitioners
and,
to
a
greater
extent,
their
amici
exhibit
a
different
concern.
They
suggest
that
recognition
of
a
screening
role
for
the
judge
that
allows
for
the
exclusion
of
"
invalid"
evidence
will
sanction
a
stifling
and
repressive
scientific
orthodoxy
and
will
be
inimical
to
the
search
for
truth.
See,
e.
g.,
Brief
for
Ronald
Bayer
et
al.
as
Amici
Curiae.
It
is
true
that
open
debate
is
an
essential
part
of
both
legal
and
scientific
analyses.
Yet
there
are
important
differences
between
the
quest
for
truth
in
the
courtroom
and
the
quest
*
597
for
truth
in
the
laboratory.
Scientific
conclusions
are
subject
to
perpetual
revision.
Law,
on
the
other
hand,
must
resolve
disputes
finally
and
quickly.
The
scientific
project
is
advanced
by
broad
and
wide­
ranging
consideration
of
a
multitude
of
hypotheses,
for
those
that
are
incorrect
will
eventually
be
shown
to
be
so,
and
that
in
itself
is
an
advance.
Conjectures
that
are
probably
wrong
are
of
little
use,
however,
in
the
project
of
reaching
a
quick,
final,
and
binding
legal
judgment­­
often
of
great
consequence­­
about
a
particular
set
of
events
in
the
past.
We
recognize
that,
in
practice,
a
gatekeeping
role
for
the
judge,
no
matter
how
flexible,
inevitably
on
occasion
will
prevent
the
jury
from
learning
of
authentic
**
2799
insights
and
innovations.
That,
nevertheless,
is
the
balance
that
is
struck
by
Rules
of
Evidence
designed
not
for
the
exhaustive
search
for
cosmic
understanding
but
for
the
particularized
resolution
of
legal
disputes.
[
FN13]

FN13.
This
is
not
to
say
that
judicial
interpretation,
as
opposed
to
adjudicative
factfinding,
does
not
share
basic
characteristics
of
the
scientific
endeavor:
"
The
work
of
a
judge
is
in
one
sense
enduring
and
in
another
ephemeral....
In
the
endless
process
of
testing
and
retesting,
there
is
a
constant
rejection
of
the
dross
and
a
constant
retention
of
whatever
is
pure
and
sound
and
fine."
B.
Cardozo,
The
Nature
of
the
Judicial
Process
178,
179
(
1921).
113
S.
Ct.
2786
Page
18
125
L.
Ed.
2d
469,
61
USLW
4805,
27
U.
S.
P.
Q.
2d
1200,
23
Envtl.
L.
Rep.
20,979,
37
Fed.
R.
Evid.
Serv.
1,
Prod.
Liab.
Rep.
(
CCH)
P
13,494
(
Cite
as:
509
U.
S.
579,
113
S.
Ct.
2786)

Copr.
©
West
2002
No
Claim
to
Orig.
U.
S.
Govt.
Works
IV
To
summarize:
"
General
acceptance"
is
not
a
necessary
precondition
to
the
admissibility
of
scientific
evidence
under
the
Federal
Rules
of
Evidence,
but
the
Rules
of
Evidence­­
especially
Rule
702­­
do
assign
to
the
trial
judge
the
task
of
ensuring
that
an
expert's
testimony
both
rests
on
a
reliable
foundation
and
is
relevant
to
the
task
at
hand.
Pertinent
evidence
based
on
scientifically
valid
principles
will
satisfy
those
demands.

The
inquiries
of
the
District
Court
and
the
Court
of
Appeals
focused
almost
exclusively
on
"
general
acceptance,"
as
gauged
by
publication
and
the
decisions
of
other
courts.
Accordingly,
*
598
the
judgment
of
the
Court
of
Appeals
is
vacated,
and
the
case
is
remanded
for
further
proceedings
consistent
with
this
opinion.

It
is
so
ordered.

Chief
Justice
REHNQUIST,
with
whom
Justice
STEVENS
joins,
concurring
in
part
and
dissenting
in
part.

The
petition
for
certiorari
in
this
case
presents
two
questions:
first,
whether
the
rule
of
Frye
v.
United
States,
54
App.
D.
C.
46,
293
F.
1013
(
1923),
remains
good
law
after
the
enactment
of
the
Federal
Rules
of
Evidence;
and
second,
if
Frye
remains
valid,
whether
it
requires
expert
scientific
testimony
to
have
been
subjected
to
a
peer
review
process
in
order
to
be
admissible.
The
Court
concludes,
correctly
in
my
view,
that
the
Frye
rule
did
not
survive
the
enactment
of
the
Federal
Rules
of
Evidence,
and
I
therefore
join
Parts
I
and
II­
A
of
its
opinion.
The
second
question
presented
in
the
petition
for
certiorari
necessarily
is
mooted
by
this
holding,
but
the
Court
nonetheless
proceeds
to
construe
Rules
702
and
703
very
much
in
the
abstract,
and
then
offers
some
"
general
observations."
Ante,
at
2796.

"
General
observations"
by
this
Court
customarily
carry
great
weight
with
lower
federal
courts,
but
the
ones
offered
here
suffer
from
the
flaw
common
to
most
such
observations­­
they
are
not
applied
to
deciding
whether
particular
testimony
was
or
was
not
admissible,
and
therefore
they
tend
to
be
not
only
general,
but
vague
and
abstract.
This
is
particularly
unfortunate
in
a
case
such
as
this,
where
the
ultimate
legal
question
depends
on
an
appreciation
of
one
or
more
bodies
of
knowledge
not
judicially
noticeable,
and
subject
to
different
interpretations
in
the
briefs
of
the
parties
and
their
amici.
Twenty­
two
amicus
briefs
have
been
filed
in
the
case,
and
indeed
the
Court's
opinion
contains
no
fewer
than
37
citations
to
amicus
briefs
and
other
secondary
sources.

*
599
The
various
briefs
filed
in
this
case
are
markedly
different
from
typical
briefs,
in
that
large
parts
of
them
do
not
deal
with
decided
cases
or
statutory
language­­
the
sort
of
material
we
customarily
interpret.
Instead,
they
deal
with
definitions
of
scientific
knowledge,
scientific
method,
scientific
validity,
and
peer
review­­
in
short,
matters
far
afield
from
the
expertise
of
judges.
This
is
not
to
say
that
such
materials
are
not
useful
or
even
necessary
in
deciding
how
Rule
703
should
be
applied;
but
it
is
to
say
that
the
unusual
subject
matter
should
cause
us
to
proceed
with
great
caution
in
deciding
more
than
we
have
to,
because
our
reach
can
so
easily
exceed
our
grasp.

But
even
if
it
were
desirable
to
make
"
general
observations"
not
necessary
to
decide
**
2800
the
questions
presented,
I
cannot
subscribe
to
some
of
the
observations
made
by
the
Court.
In
Part
II­
B,
the
Court
concludes
that
reliability
and
relevancy
are
the
touchstones
of
the
admissibility
of
expert
testimony.
Ante,
at
2794­
95.
Federal
Rule
of
Evidence
402
provides,
as
the
Court
points
out,
that
"[
e]
vidence
which
is
not
relevant
is
not
admissible."
But
there
is
no
similar
reference
in
the
Rule
to
"
reliability."
The
Court
constructs
its
argument
by
parsing
113
S.
Ct.
2786
Page
19
125
L.
Ed.
2d
469,
61
USLW
4805,
27
U.
S.
P.
Q.
2d
1200,
23
Envtl.
L.
Rep.
20,979,
37
Fed.
R.
Evid.
Serv.
1,
Prod.
Liab.
Rep.
(
CCH)
P
13,494
(
Cite
as:
509
U.
S.
579,
113
S.
Ct.
2786)

Copr.
©
West
2002
No
Claim
to
Orig.
U.
S.
Govt.
Works
the
language
"[
i]
f
scientific,
technical,
or
other
specialized
knowledge
will
assist
the
trier
of
fact
to
understand
the
evidence
or
to
determine
a
fact
in
issue,
...
an
expert
...
may
testify
thereto...."
Fed.
Rule
Evid.
702.
It
stresses
that
the
subject
of
the
expert's
testimony
must
be
"
scientific
...
knowledge,"
and
points
out
that
"
scientific"
"
implies
a
grounding
in
the
methods
and
procedures
of
science"
and
that
the
word
"
knowledge"
"
connotes
more
than
subjective
belief
or
unsupported
speculation."
Ante,
at
2794­
95.
From
this
it
concludes
that
"
scientific
knowledge"
must
be
"
derived
by
the
scientific
method."
Ante,
at
2795.
Proposed
testimony,
we
are
told,
must
be
supported
by
"
appropriate
validation."
Ante,
at
2795.
Indeed,
in
footnote
9,
the
Court
decides
that
"[
i]
n
a
case
involving
scientific
evidence,
evidentiary*
600
reliability
will
be
based
upon
scientific
validity."
Ante,
at
2795,
n.
9
(
emphasis
in
original).

Questions
arise
simply
from
reading
this
part
of
the
Court's
opinion,
and
countless
more
questions
will
surely
arise
when
hundreds
of
district
judges
try
to
apply
its
teaching
to
particular
offers
of
expert
testimony.
Does
all
of
this
dicta
apply
to
an
expert
seeking
to
testify
on
the
basis
of
"
technical
or
other
specialized
knowledge"­­
the
other
types
of
expert
knowledge
to
which
Rule
702
applies­­
or
are
the
"
general
observations"
limited
only
to
"
scientific
knowledge"?
What
is
the
difference
between
scientific
knowledge
and
technical
knowledge;
does
Rule
702
actually
contemplate
that
the
phrase
"
scientific,
technical,
or
other
specialized
knowledge"
be
broken
down
into
numerous
subspecies
of
expertise,
or
did
its
authors
simply
pick
general
descriptive
language
covering
the
sort
of
expert
testimony
which
courts
have
customarily
received?
The
Court
speaks
of
its
confidence
that
federal
judges
can
make
a
"
preliminary
assessment
of
whether
the
reasoning
or
methodology
underlying
the
testimony
is
scientifically
valid
and
of
whether
that
reasoning
or
methodology
properly
can
be
applied
to
the
facts
in
issue."
Ante,
at
2796.
The
Court
then
states
that
a
"
key
question"
to
be
answered
in
deciding
whether
something
is
"
scientific
knowledge"
"
will
be
whether
it
can
be
(
and
has
been)
tested."
Ante,
at
2796.
Following
this
sentence
are
three
quotations
from
treatises,
which
not
only
speak
of
empirical
testing,
but
one
of
which
states
that
the
"
'
criterion
of
the
scientific
status
of
a
theory
is
its
falsifiability,
or
refutability,
or
testability,'
"
Ante,
at
2796­
97.

I
defer
to
no
one
in
my
confidence
in
federal
judges;
but
I
am
at
a
loss
to
know
what
is
meant
when
it
is
said
that
the
scientific
status
of
a
theory
depends
on
its
"
falsifiability,"
and
I
suspect
some
of
them
will
be,
too.

I
do
not
doubt
that
Rule
702
confides
to
the
judge
some
gatekeeping
responsibility
in
deciding
questions
of
the
admissibility
of
proffered
expert
testimony.
But
I
do
not
think
*
601
it
imposes
on
them
either
the
obligation
or
the
authority
to
become
amateur
scientists
in
order
to
perform
that
role.
I
think
the
Court
would
be
far
better
advised
in
this
case
to
decide
only
the
questions
presented,
and
to
leave
the
further
development
of
this
important
area
of
the
law
to
future
cases.

113
S.
Ct.
2786,
509
U.
S.
579,
125
L.
Ed.
2d
469,
61
USLW
4805,
27
U.
S.
P.
Q.
2d
1200,
23
Envtl.
L.
Rep.
20,979,
37
Fed.
R.
Evid.
Serv.
1,
Prod.
Liab.
Rep.
(
CCH)
P
13,494
END
OF
DOCUMENT
