To the Editor: Dr. Matejkowski et al. are correct that he and his coauthors did not claim in their study that individuals with severe and untreated psychiatric disorders "are responsible for approximately 10% of the homicides in the United States." That was my conclusion based on their data and on two previous studies. Among 518 offenders convicted of murder in Indiana, Matejkowski et al. said that 27 had schizophrenia, 14 had mania or bipolar disorder, 14 had another psychiatric disorder, and 58 had major depression (1). The authors themselves claimed that 95 of them, or 19%, had "severe mental illness." Among those for whom a treatment history was known, 43% had never been treated or had been treated only once.

Such findings are consistent with a California study by Wilcox (2), who reported that seven of 71 individuals (10%) who committed homicides were diagnosed with schizophrenia, and almost all were untreated at the time of the crime. The findings are also consistent with a New York study by Grunberg et al. (3, 4) that reported that eight of 48 individuals (17%) who committed homicides were diagnosed with schizophrenia. Fourteen studies from other countries reported that individuals with severe psychiatric disorders committed on average 9.3% of homicides (5).

Given these studies and the absence of any contradictory data, I stand by my original claim that individuals with severe and untreated psychiatric disorders "are responsible for approximately 10% of the homicides in the United States." Despite the importance of this issue, neither the National Institute of Mental Health nor the Substance Abuse and Mental Health Services Administration has funded a study to obtain more definitive U.S. data on this issue.