Kessler Psychological Distress Scale (K6)

Introduction

The Kessler Psychological Distress Scale (K6) is a six-question survey that screens for serious psychological distress over the past four weeks. Ronald C. Kessler, PhD, of Harvard Medical School, and colleagues developed it alongside the longer K10. The K6 is merely a truncated form of the K10 in which four questions are deleted. Its purpose is to quickly identify people likely to have a serious mental illness. In testing, the six-question scale was found to be at least as sensitive as the ten-question scale for discriminating between cases and non-cases of serious mental illness. It’s widely used in national health monitoring: the K6 is now included in the core of the U.S. National Health Interview Survey as well as in the annual National Household Survey on Drug Abuse.

The Kessler Psychological Distress Scale (K10) is a 10-question survey that measures general psychological distress, such as anxiety and depressive symptoms, over the past four weeks. Ronald C. Kessler, PhD, a professor at Harvard Medical School, and colleagues developed it in the early 2000s. It was 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. The scale was designed to be sensitive around the threshold for the clinically significant range of distress, to help distinguish cases of serious mental illness from non-cases. It’s widely used in primary care, mental health services, and population surveys. It’s included in the Australian and Canadian equivalents of the U.S. national health survey, and in all the national surveys of the World Mental Health Initiative. Both the K6 and K10 measures overall distress. It doesn’t diagnose a specific disorder.

What it asks

Patients rate how often in the past four weeks they felt: nervous; hopeless; restless or fidgety; so depressed that nothing could cheer them up; that everything was an effort; and worthless. Each item uses the same five answers, from “none of the time” to “all of the time.”

How it’s scored

This tool uses Australian scoring. Each answer is scored from 1 (“none of the time”) to 5 (“all of the time”), and the six scores are added for a total from 6 to 30. Higher scores mean more distress. In the US, the same answers are scored 0 to 4, for a total from 0 to 24. The Australian system results in a score range of 6-30 for the K6, compared with 0–24 in the US system. The Australian total is always exactly 6 points higher than the US total for the same answers.

Higher scores mean higher levels of distress.

How results are interpreted

The K6 uses a single cutoff:

On Australian scoring, the optimal cut point on the K6 is 6-18 versus 19+. That corresponds to the widely cited US cutoff of 13 or more on the 0–24 scale. A score of 19 or more suggests further clinical assessment is warranted, but it isn’t a diagnosis. Unlike the K10, the K6 has no official mild, moderate, or severe bands.

• This is a screening instrument and practitioners should make a clinical judgement as to whether a person needs further assessment and treatment.

Limitations

The cutoff was designed for general population screening. Kessler notes that this cut point is optimal only in a population that has the same prevalence as the total US population, so it may perform differently in clinics where mental illness is more or less common. Like the K10, the K6 measures overall distress rather than a specific condition, and it has no question about suicidal thoughts, so it can’t be used to assess safety. A score below the cutoff doesn’t rule out distress or a mental health condition.

Kessler, R. C., Andrews, G., Colpe, L. J., Hiripi, E., Mroczek, D. K., Normand, S.-L. T., Walters, E. E., & Zaslavsky, A. M. (2002). Short screening scales to monitor population prevalences and trends in non-specific psychological distress. Psychological Medicine, 32(6), 959–976.