abused and filed a police complaint subsequently tes-
tify at trial that the defendant was not the source of her
injuries. Prosecutors have successfully introduced
BWS for the purpose of impeaching the witness’s tes-
timony and thus explaining why she changed her
story. But evidence of past battering, which is symp-
tomatic of BWS, is likely to be used by the trier of fact
substantively—that is, for the prohibited purpose of
proving that the defendant assaulted the witness on
the occasion in question.Future Behavior
The subject of predicting future behavior raises a host
of issues involving both the reliability of the claimed
expertise and the scope of the substantive and proce-
dural rules that apply to that expertise. The most usual
prediction involves a person’s likelihood of behaving
violently. Courts call for expert predictions of future
violence in a wide assortment of legal contexts,
including ordinary civil commitment hearings, capital
sentencing hearings, commitment hearings following
a verdict of not guilty by reason of insanity, commit-
ment hearings following a determination of incompe-
tency to stand trial, parole and probation hearings, and
hearings under community notification laws for “sex-
ual predators.” Yet courts regularly remark that pre-
dicting future behavior is inherently difficult, and
most research indicates that psychiatrists and psychol-
ogists do not do it very well. Indeed, this area of the
law presents a paradox in which judges seemingly
take the most lenient approach toward scientific evi-
dence involving some of the most controversial sci-
ence to enter the courtroom.
As a general procedural matter, courts ordinarily do
not apply evidentiary rules of admissibility to predic-
tions of violence. In many areas, such as capital sen-
tencing or probation hearings, rules of evidence do not
apply. In other areas, such as commitment hearings or
community notification determinations, evidence rules
ostensibly apply, but courts proceed, either implicitly or
explicitly, on the basis that the substantive law requires
psychological expert testimony. Hence, the expertise is
admissible not because it is deemed relevant and reli-
able but because it is deemed necessary under the sub-
stantive law that applies to the case.
Although evidence rules might not apply to predic-
tions of violence, constitutional safeguards do. The
Supreme Court, however, rejected a constitutional
challenge to predictions of violence in Barefoot v.Estelle(1983), the only case it has heard on the sub-
ject. The BarefootCourt rejected the defendant’s con-
tention, backed by an amicus brief submitted by the
American Psychiatric Association (APA), that predic-
tions of future violence were unreliable. The Court
argued that “neither petitioner nor the [American
Psychiatric] Association suggests that psychiatrists
are always wrong with respect to future dangerous-
ness, only most of the time.”
Despite the APA’s statement that psychiatrists can-
not distinguish accurate from inaccurate predictions,
the Court believed juries could do so. “We are uncon-
vinced... that the adversary process cannot be
trusted to sort out the reliable from the unreliable evi-
dence and opinion about future dangerousness, partic-
ularly when the convicted felon has the opportunity to
present his own side of the case.” Yet as Justice
Blackmun pointed out in dissent, this observation
“misses the point completely,” for “one can only won-
der how juries are to separate valid from invalid expert
opinion when the ‘experts’ themselves are so obvi-
ously unable to do so.”Current Mental State
A seemingly less daunting task for psychologists than
describing past mental states, characterizing past
behavior, or predicting future behavior involves
assessing current mental states. The law seeks such
mental assessments in a variety of contexts, including
the competency of defendants to be tried and the com-
petency of those convicted of capital offenses to be
executed. In the former category, the issue involves
whether a defendant is able to assist in his or her own
defense and comprehends the nature of the proceed-
ings and the charges against him or her. In the latter
category, the issue involves whether the condemned
person comprehends the State’s reasons for executing
him or her and understands what is about to occur.
Competency assessments are typically decided by
judges as a matter of law. Experts usually rely on a
mixture of clinical judgment and standardized tests,
which may range widely in terms of reliability and
construct validity. Indeed, this area has not been the
subject of close or critical review by the courts, and
there appear to be few guidelines for courts to ensure
the receipt of relevant and valid scientific opinion. In
general, evidence rules do not apply to this subject
and courts do not employ evidentiary standards of
reliability to expert opinion regarding current mentalExpert Psychological Testimony——— 269E-Cutler (Encyc)-45463.qxd 11/18/2007 12:42 PM Page 269