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 (1979).
  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 that has been able to attract only
minimal support within the community,- Downing, supra, at 1238, may
properly be viewed with skepticism.
  The inquiry envisioned by Rule 702 is, we emphasize, a flexible one.
Its overarching subject is the scientific validity-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.
  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 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 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.
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