KEY NOTES:
 A mental disorder is a syndrome characterized by clinically
significant disturbance in an individual’s cognition, emotion
regulation, or behavior that reflects a dysfunction in the
psychological, biological, or developmental processes underlying
mental functioning. Mental disorders are usually associated with
significant distress in social, occupational, or other important
activities. An expectable or culturally approved response to a
common stressor or loss, such as the death of a loved one, is not a
mental disorder. Socially deviant behavior (e.g., political, religious,
or sexual) and conflicts that are primarily between the individual
and society are not mental disorders unless the deviance or conflict
results from a dysfunction in the individual, as described above.
 As a bridge between the issues of treatment and prediction, which will be
addressed shortly, let us consider the causal relation between mental disorder
and criminal conduct. The most important thing to recognize for lawyers and
policymakers is that mental disorders that apparently play a causal role do not
turn the person into an automaton. People with mental disorders act for reasons
just like people without such disorders. Consider Daniel M’Naghten, for example,
a 19th-century Scotsman who was delusional and believed the Tory Party was
persecuting him and was attempting to kill him. He intended to kill British Prime
Minister Robert Peel to save his own life, and acted on that intent (although,
in the event, he killed Peel’s private secretary, Edward Drummond, who was
riding in the prime minister’s carriage that day). Abnormal perceptions or beliefs
motivate people with mental disorders and they then act on those beliefs. Their
criminal acts should not be understood mechanistically, like a fever that spikes
as the result of an underlying infection. Causation should be understood in this
context in terms of assessing the defendant’s reasons for action.
Finally, simply because a mental disorder played a causal role in explaining
criminal behavior, it does not follow that the person could not control that
behavior. The notion of loss of control of action is notoriously fraught. A
minority of jurisdictions have a control test for legal insanity in addition to a
cognitive test, and the Supreme Court has approved the use of control criteria
for sexual-predator commitments.9 But the meaning of these tests—at least to
the extent that a defendant’s control of his behavior is considered independent
of his rationality—remains conceptually and empirically unclear. For these
reasons, both the American Psychiatric Association and the American Bar
Association recommended abolition of control tests for legal insanity.
Investigation of good studies discloses a far weaker connection between
major mental disorder and criminality than many people stereotypically
assume. Most people with mental disorder do not engage in serious criminal
behavior and are more likely to be victims of violence than perpetrators. The
rate of serious criminal behavior among people with major mental disorder
is approximately the same as the population as a whole—about 3% to 4%—
unless the person is also abusing substances, which does increase the rate. This
is unsurprising because people with serious disorders do have higher rates of
substance-use problems, probably because they are self-medicating to deal
with the pain of mental disorder and related problems. Nonetheless, even in
this co-morbid population—people with major mental disorder and substance
abuse—the rate of serious criminal behavior is low.10 Moreover, the association
between psychotic states and violent behavior is weak and inconsistent. The
strongest association between mental disorder and violent conduct is selfharm,
especially suicide by gun.11 This is tragic, but not a criminal justice issue.
In short, there are clear cases in which mentally abnormal thoughts and
moods may be causally related to criminal conduct, but for the most part,
major mental disorder is not a major cause of crime. There is a powerful moral
and social argument that better mental-health services should be provided to
the population at large and especially to those without the resources to afford
private care. It is a mistake, however, to believe that more aggressive mentalhealth
care, including increased use of involuntary civil commitment or
compulsory treatment, will make much inroad in preventing serious criminal
behavior. Such interventions, which often involve substantial deprivations of
liberty, may have positive mental-health outcomes for some sufferers, but they
will have slight impact on criminal conduct.