Encyclopedia of Psychology and Law

impact of varying case facts on decision making in

insanity cases. Mock jurors seem to construe case

information differently depending on their prior

beliefs and attitudes. As noted above, there is a ten-

dency for jurors in insanity defense cases to rely more

on their own notions of insanity than on the facts of

the case. The type of mental illness can be influential,

and much research has focused on schizophrenic

defendants. Some case facts are also influential in

insanity verdicts. For example, some research has

found that defendants who had been more reckless,

committed more gruesome crimes, and behaved with

premeditation were found guilty more often.

Research has also investigated the impact of the

personal characteristics of the jurors themselves. The

importance of personal contact with mental illness

(either through a personal experience or that of a rel-

ative or a friend) has been examined, with mixed

results. For example, contact with people with mental

illness has a somewhat positive effect on attitudes

toward mental illness. Studies have shown that college

students who had direct interactions with people suf-

fering from depression or psychosis made more posi-

tive attributions about the causes of these illnesses. On

the other hand, some research has found that those

suffering from mental illnesses were less accepting of

others who had mental illnesses. Juror gender has also

been found to exert an influence on verdict in a lim-

ited number of studies; there is some indication that

females may be more accepting than males of the

insanity defense and of mental illness as a factor in

determining criminal responsibility.

Expert Witnesses and

the Insanity Defense

Expert testimony is typically proffered in trials where

the defendant is raising an insanity defense. The typi-

cal successful insanity defense requires a showing of

significant mental illness or impairment through expert

testimony. The role of experts in insanity defense trials

is somewhat unique. There has been substantial con-

troversy about the role of expert psychological testi-

mony in insanity defense trials, and some have

advocated doing away with experts in these cases. The

law places a number of constraints on experts in insan-

ity trials. Psychologists in most instances testify about

a diagnosis for the defendant and the symptoms asso-

ciated with that diagnosis, and they give their opinions

regarding the defendant’s ability to understand the

difference between right and wrong. However, after

the Hinkley case, the Federal Rules of Evidence were

amended to disallow expert mental health testimony

on the ultimate issue—whether or not the defendant

was sane or insane at the time of the alleged offense.

This decision was left to the trier of the fact. Limited

research has examined the effect of expert testimony in

general or of ultimate opinion testimony on juror deci-

sion making. A consistent finding is that the ultimate

opinions proffered by experts do not have a significant

effect on decision making, contrary to the concerns

underlying their prohibition.

Jennifer Groscup and Tarika Daftary

See alsoCriminal Responsibility, Assessment of; Criminal

Responsibility, Defenses and Standards; Expert

Psychological Testimony; Extreme Emotional

Disturbance; Guilty but Mentally Ill Verdict; Insanity

Defense Reform Act (IDRA); Mental Illness and the

Death Penalty; M’Naghten Standard

Further Readings

Finkel, N. J. (1988). Insanity on trial.New York: Plenum

Press.

Hans, V. P., & Slater, D. (1984). “Plain crazy”: Lay

definitions of legal insanity. International Journal of Law

and Psychiatry, 7,105–114.

Perlin, M. L. (1996). The insanity defense: Deconstructing

the myths and reconstructing jurisprudence. In B. D. Sales

& D. Shuman (Eds.),Law, mental health, and mental

disorder(pp. 341–359). Belmont, CA: Thomson

Brooks/Cole.

Poulson, R. L., Braithwaite, R. L., & Brondino, M. J. (1997).

Mock jurors’ insanity defense verdict selections: The role

of evidence, attitudes, and verdict options. Journal of

Social Behavior & Personality, 12,743–758.

Zapf, P. A., Golding, S. L., & Roesch, R. (2006). Criminal

responsibility and the insanity defense. In I. B. Weiner &

A. K. Hess (Eds.),The handbook of forensic psychology

(3rd ed., pp. 332–363). Hoboken, NJ: Wiley.

INSANITYDEFENSE

REFORMACT(IDRA)

The Insanity Defense Reform Act (IDRA), passed by

Congress in 1984, imposed a uniform standard for

legal insanity that applies in all federal trials in which

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