The K10 and K6 scales were developed with support from the U.S. government's National Center for Health Statistics for use in the redesigned U.S. National Health Interview Survey (NHIS). The K6 scale is a truncated version of the K10 in which four questions are deleted. The K10 is a 10-question scale originally developed to provide an efficient population-level screen for serious mental illness (SMI) in the USA. Evidence that the six-item shortened version performed as well as the original 10-item version led to rapid dissemination and replicated validation of the K6 in a number of other countries. The K6 is now included in the core of the NHIS as well as in the annual National Household Survey on Drug Abuse. The K6 is now often included in large general-purpose government health tracking surveys.

This is a 10 question assessment intended to measure levels of psychological distress based on questions about anxiety and depressive symptoms experienced in the past 4 weeks. The results of clinical trials have supported the validity of this assessment in discriminating between cases and non-cases of severe mental illness.