How well did a six-question screen identify serious mental illness across 14 countries?

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Researchers reported on the background and performance of the K6 screening scale for serious mental illness (SMI) in the World Health Organization (WHO) World Mental Health (WMH) surveys. K6 is a six-item scale developed as a brief, valid screen for SMI as defined by the Diagnostic and Statistical Manual of Mental Disorders, fourth edition (DSM-IV), based on criteria in the US ADAMHA Reorganization Act.

Previous methodological studies had found good K6 validity in several countries, but optimal scoring rules had not been proposed. The researchers presented such rules using K6 data from nationally or regionally representative WMH surveys in 14 countries, with a combined 41,770 respondents. Twelve-month prevalence of DSM-IV SMI was assessed using the fully structured WHO Composite International Diagnostic Interview.

The team used nested logistic regression to estimate each respondent’s predicted probability of SMI from their K6 score, considering whether concordance could vary by age, gender, education and country. Concordance was assessed using the area under the receiver operating characteristic curve and was generally substantial: the median was 0.83, the range was 0.76–0.89, and the interquartile range was 0.81–0.85. Based on these results, the researchers presented optimal scaling rules for investigators using K6 in the countries studied.