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(October 1, 2019) Individuals with serious mental illness may be treated differently by the criminal justice and legal systems, according to new research, which may contribute to the higher prevalence of this population in jails and prisons.

A team of researchers from New York recently analyzed state data to determine the effect of serious mental illness on the severity of consequences endured by defendants following arrest. The researchers identified all individuals arrested for a misdemeanor or felony between January 2010 and 2013 from the state’s Division of Criminal Justice records. For individuals with multiple arrests, only the first arrest was considered in the analysis.

Arrest records were then matched with Medicaid billing records and admission and discharge records from the Office of Mental Health using specialized computer software. This process allowed the researchers to identify arrestees who received public mental health treatment in the year prior to their arrest. Individuals were considered to have serious mental illness if they were diagnosed and treated for schizophrenia, schizoaffective disorder, another psychotic disorder, bipolar disorder, manic affective disorder, or major depressive disorder at least one time in the analysis period.

Study Results

Of all individuals facing a misdemeanor charge, 20% ultimately received a jail sentence while 6% had been diagnosed with a serious mental illness in the year before their arrest. Based on analysis of the data, the presence of serious mental illness increased the likelihood of incarceration following a misdemeanor by more than 50%, even when controlling for variables such as race, violence of the offense, and prior arrest history.

For felony arrests, 12% of individuals received a prison sentence for their offense whereas 4% had been diagnosed with a serious mental illness in the past year. Serious mental illness was not shown to increase the likelihood of incarceration for felony offenses on its own. However, the researchers found that the presence of serious mental illness did have an effect when combined with other variables.

For example, the interaction of serious mental illness with violent felonies greatly increased the likelihood the defendant would receive a prison sentence. While individuals without serious mental illness who committed violent felonies were 68% more likely to face incarceration, defendants with serious mental illness who committed similar crimes were 114% more likely to be sentenced to prison. The authors suggest this difference could be attributable to elevated concerns by those involved in the sentencing process about the capacity of individuals with serious mental illness for future violence. Conversely, concerning race, the presence of serious mental illness decreased the likelihood of receiving a prison sentence for nonwhite defendants.

There are a number of considerations to keep in mind when interpreting the study findings. The authors note that the percentage of individuals with serious mental illness in the defendant population was lower than estimates within correctional facilities. This discrepancy could be due to multiple factors, including the longer sentences and higher re-arrest rates faced by individuals with serious mental illness. Additionally, not all defendants with symptoms or diagnoses of serious mental illness would have sought treatment in the year before their arrest, and therefore would not be part of the sample for the analysis.

The findings offer mixed results about the effect of serious mental illness on the sentencing process for different types of crimes. However, the results for misdemeanor offenses may help explain the high prevalence of individuals with serious mental illness in correctional facilities, write the study authors. According to prior research, non-legal factors, including individual characteristics such as the presence of mental illness, are most influential in lower-level cases when more discretion is involved in sentencing. More research is needed on the effects of other variables such as socioeconomic status and pretrial incarceration as related to serious mental illness and sentencing outcomes.

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