Kessler Psychological Distress Scale (K6): Scoring, Cutoffs & Interpretation

What this scale measures.

The K6 measures non-specific psychological distress over the past 30 days. Its six items ask how often the respondent felt nervous, hopeless, restless or fidgety, so depressed that nothing could cheer them up, that everything was an effort, and worthless. Each item is rated on a five-point frequency scale from "none of the time" (0) to "all of the time" (4), giving a total of 0–24. Rather than mapping onto one diagnosis, the K6 captures the shared emotional core that runs across mood and anxiety disorders.

Because it is short, free and deliberately non-specific, the K6 is one of the most widely used population screens for mental illness in the world. It sits in major government health surveys - including the US National Health Interview Survey and the WHO World Mental Health surveys - and doubles in clinics as a rapid triage measure when the question is "is this person in significant distress?" rather than "which disorder is this?".

Where it comes from.

The K6 and its ten-item sibling the K10 were developed by Ronald Kessler and colleagues at Harvard for the US National Health Interview Survey, published in Psychological Medicine in 2002. Using item response theory, the team screened a large pool of candidate items and retained the six that discriminated most precisely in the clinical range of the distress continuum - the region that matters when deciding who needs assessment.

A companion 2003 paper in Archives of General Psychiatry calibrated the K6 as a screen for serious mental illness (SMI) in the general population, establishing the ≥13 cutoff still used by US federal surveys to estimate SMI prevalence. The K6 was designed for population surveillance first, and its brevity later made it a natural fit for waiting-room screening and repeated monitoring.

How scoring works.

Sum the six items (each 0–4) for a total of 0–24. Scores of 13 or above indicate probable serious psychological distress and a high likelihood of meeting criteria for a serious mental illness (Kessler et al., 2003). Prochaska and colleagues (2012) validated a lower threshold: scores of 5–12 mark moderate mental distress associated with genuine treatment need, so a K6 of 5 or more merits clinical attention even though it falls below the SMI cutoff. Scores of 0–4 suggest low distress. Note that some countries (notably Australia) score each item 1–5, giving a 6–30 range - check which convention a report uses before comparing numbers.

How well it performs.

Internal consistency is high across populations, with Cronbach's alpha typically reported between 0.89 and 0.93. Against structured diagnostic interviews, validation studies report sensitivity around 0.83 and specificity around 0.79 at the 12/13 threshold, with a negative predictive value above 0.90 - good performance for a six-item screen. The 2012 California Health Interview Survey study (n = 50,880) validated the moderate-distress band, and the K6's inclusion in the WHO World Mental Health surveys has produced validation data across dozens of countries and languages.

How it compares to the alternatives.

Right tool, wrong tool.

Reading the score with care.

No standard error of measurement or minimal clinically important difference is established for the K6 in routine clinical use, so interpret score changes cautiously: small shifts of a point or two are within plausible measurement noise, and movement across the 5 and 13 thresholds matters more than the raw change. The scale is most precise in the upper (clinical) range of distress, where its items were selected to discriminate - floor effects make it less informative for distinguishing degrees of good mental health.

What it cannot tell you.

It is a screen, not a diagnostic instrument; a high score says "assess this person", not what they have. The 30-day window can miss episodic conditions. It does not cover suicidality, psychosis, mania or substance use. The dual scoring conventions (0–24 vs 6–30) cause real-world confusion when comparing reports. And because the items were tuned to the clinical range, it discriminates poorly among people with low distress.

Common questions from clinicians

FAQ

References

Source literature.

1. [1]Kessler RC, Andrews G, Colpe LJ, et al. Short screening scales to monitor population prevalences and trends in non-specific psychological distress. Psychological Medicine. 2002;32(6):959-976 (2002) ↩
2. [2]Kessler RC, Barker PR, Colpe LJ, et al. Screening for serious mental illness in the general population. Archives of General Psychiatry. 2003;60(2):184-189 (2003) ↩
3. [3]Prochaska JJ, Sung HY, Max W, Shi Y, Ong M Validity study of the K6 scale as a measure of moderate mental distress based on mental health treatment need and utilization. International Journal of Methods in Psychiatric Research. 2012;21(2):88-97 (2012) ↩
4. [4]Furukawa TA, Kessler RC, Slade T, Andrews G The performance of the K6 and K10 screening scales for psychological distress in the Australian National Survey of Mental Health and Well-Being. Psychological Medicine. 2003;33(2):357-362 (PMID: 12622315) (2003) ↩
5. [5]Kim G, DeCoster J, Chiriboga DA, et al. Validation of the K6/K10 scales of psychological distress and their optimal cutoff scores for older Koreans (2016) ↩