Homicide-suicide events can be classified into eight replicable subtypes

Researchers have found eight replicable homicide-suicide subtypes, according to study results published in Journal of Clinical Psychiatry.

Risk for each of these subtypes was linked to certain demographic and clinical characteristics.

“The purpose of this study was to overcome some limitations of previous efforts by characterizing homicide-suicide decedents with a large-scale database more nationally representative than previous studies and developing and characterizing the first empirically derived typology for homicide-suicide decedents in the United States, using unsupervised machine learning,” Joshua T. Jordan, PhD, of the department of psychology at the Dominican University of California, and Dale E. McNiel, PhD, of the department of psychiatry and behavioral sciences at the University of California, San Francisco, wrote.

Jordan and McNiel analyzed data from CDC’s National Violent Death Reporting System (NVDRS) between 2003 and 2015 in 27 states. They included 2,447 homicide-suicide decedents who were aged 18 years or older, were the only victim and suspect involved and had a known relationship to the victim or victims. The circumstances surrounding the event needed to be known for the event to be included. The researchers classified decedents according to precipitating circumstances and victim types using unsupervised machine learning.

Results showed cross-validation in a holdout sample of eight homicide-suicide subtypes. Of these, three consisted of only victims of intimate partners, three included a single victim and two subtypes were multivictim, with one identified as familicide and the other as indiscriminate killing that often included an intimate partner. Demographic and other characteristics differentiated subtypes. Across subtypes, relationship problems precipitated between 60% and 92% of homicide-suicides and mental health problems precipitated between 7% and 72% of decedents.

“As implementation of the NVDRS continues to expand across all states, future efforts should focus on replicating these findings and, if possible, link psychological autopsy data to the NVDRS,” Jordan and colleagues wrote. “In summary, the present study represents the first known effort to use empirical data to derive an empirical typology of homicide-suicide in the United States and is therefore an important step in further understanding this rare and catastrophic phenomenon.”