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Finally, the MacArthur researchers estimated several
different risk assessment models in an attempt to obtain
multiple risk assessments for each case. That is, they
chose a number of different risk factors to be the lead
variable on which a classification tree was constructed.
In attempting to combine these multiple risk estimates,
they began to conceive of each separate risk estimate as
an indicator of the underlying construct of interest—
violence risk. The basic idea was that patients who
scored in the high-risk category on many classification
trees were more likely to be violent than patients who
scored in the high-risk category on fewer classification
trees. (And analogously, patients who scored in the
low-risk category on many classification trees were less
likely to be violent than patients who scored in the low-
risk category on fewer classification trees.)Specific Research Methods
in the MacArthur Study
More than 1,000 admissions were sampled from acute
civil inpatient facilities in Pittsburgh, Pennsylvania,
Kansas City, Missouri, and Worcester, Massachusetts.
The MacArthur researchers selected English-speaking
patients between the ages of 18 and 40, who were of
White, Black, or Hispanic ethnicity, and who had a
chart diagnosis of thought or affective disorder, sub-
stance abuse, or personality disorder. The median
length of stay was 9 days. After giving informed con-
sent to participate in the research, the patient was
interviewed in the hospital by both a research inter-
viewer and a research clinician to assess him or her on
each of the risk factors.
Three sources of information were used in the
MacArthur Study to ascertain the occurrence and
details of a violent incident in the community.
Interviews with patients, interviews with collateral
individuals (i.e., persons named by the patient as
someone who would know what was going on in his
or her life), and official sources of information (arrest
and hospital records) were all coded and compared.
Patients and collaterals were interviewed twice over
the first 20 weeks—approximately 4 to 5 months—
from the date of hospital discharge.
Violence to others was defined to include acts of
battery that resulted in physical injury, sexual assaults,
assaultive acts that involved the use of a weapon, or
threats made with a weapon in hand.Results of the MacArthur Study
At least one violent act during the first 20 weeks after
discharge from the hospital was committed by 18.7%
of the patients in the MacArthur Study. Of the 134
risk factors measured in the hospital, approximately
half had a statistically significant bivariate relation-
ship with later violence in the community (p< .05).
Some examples of specific risk factors that were—or
were not—significantly related to violence are
as follows:Gender:Men were somewhat more likely than women
to be violent, but the difference was not large. Violence
by women was more likely than violence by men to be
directed against family members and to occur at home
and less likely to result in medical treatment or arrest.
Prior violence:All measures of prior violence—self-
report, arrest records, and hospital records—were
strongly related to future violence.Childhood experiences:The seriousness and frequency
of having been physically abused as a child predicted
subsequent violent behavior, as did having a parent—
particularly a father—who was a substance abuser or a
criminal.
Diagnosis:A diagnosis of a major mental disorder—
especially a diagnosis of schizophrenia—was associated
with a lowerrate of violence than a diagnosis of a person-
ality or adjustment disorder. A co-occurring diagnosis of
substance abuse was strongly predictive of violence.Psychopathy:Psychopathy, as measured by a screening
version of the Hare Psychopathy Checklist, was more
strongly associated with violence than any other risk
factor. The “antisocial behavior” component of psy-
chopathy, rather than the “emotional detachment” com-
ponent, accounted for most of this relationship.
Delusions:The presence of delusions—or the type of
delusions or the content of delusions—was not associ-
ated with violence. A generally “suspicious” attitude
toward others was related to later violence.Hallucinations:Neither hallucinations in general nor
“command” hallucinations per se elevated the risk of
violence. If voices specifically commanded a violent
act, however, the likelihood of violence was increased.
Violent thoughts:Thinking or daydreaming about harm-
ing others was associated with violence, particularly if
the thoughts or daydreams were persistent.MacArthur Violence Risk Assessment Study——— 469M-Cutler (Encyc)-45463.qxd 11/18/2007 12:43 PM Page 469