K6: Kessler Psychological Distress Scale, 6-item version

What this assessment is

The K6 is a six-item screen of nonspecific psychological distress over the past 30 days. Standard scoring runs from 0 to 24. In U.S. surveillance, 13 or more marks serious psychological distress, but it is not a diagnosis.

Ronald Kessler and colleagues developed it as the short form of the 10-item K10. The instrument developer describes the K6 as six questions taken from the longer scale rather than a separate question set.

The scale was designed for population surveys, where a small set of questions can help estimate how common serious distress is across a large group. It does not identify a specific disorder.

Who it was designed for

The K6 was developed for the redesigned U.S. National Health Interview Survey, with the main purpose of estimating the prevalence of serious mental illness in the general adult population using few questions.

Researchers also use it to compare distress across groups and over time. Before comparing results, check that the wording, recall period, scoring convention, administration method, and missing-data rule are comparable.

The original development study tested both the K6 and K10 in general population surveys. The published study describes the K6 as a short form embedded within the K10.

How it is administered

The developer provides self-administered and interviewer-administered versions. The standard English forms ask about the past 30 days and use five frequency choices for each item.

Some forms add questions about persistence, daily functioning, healthcare use, and physical causes. The developer's guidance states that those extra questions do not contribute to the K6 total.

The developer says that changing the recall period to seven days should not cause significant interpretation problems. Report the timeframe and compare results collected over comparable periods.

What it measures

The K6 measures nonspecific psychological distress. It records frequency but cannot identify a cause. A total cannot show whether distress comes from illness, loss, work, relationships, treatment changes, or another source.

It also cannot separate one mental health condition from another.

How scoring works

The official scoring guide describes two common coding systems:

• The developer's method assigns 0 to 4 points per response and produces a total from 0 to 24.
• The Australian method assigns 1 to 5 points per response and produces a total from 6 to 30.

Higher totals indicate more frequent psychological distress in both systems. The same response pattern is six points higher under the Australian method, so every report should state which range it uses.

The developer does not prescribe one universal missing-response method. In the National Center for Health Statistics method, all six responses must be present before a total is calculated.

How to interpret a K6 score

The National Center for Health Statistics uses 13 or more on the 0 to 24 scale to define serious psychological distress in U.S. adult surveillance. The equivalent boundary is 19 or more on the 6 to 30 scale.

The original calibration study selected the 13-point boundary to balance false positives and false negatives for serious mental illness in a small local sample. In populations with a different prevalence, the threshold's predictive values and usefulness for individual classification will differ. Neither use makes 13 a diagnosis.

A K6 score is not a diagnosis. It cannot confirm or rule out serious mental illness, because diagnosis requires a clinical assessment that considers symptoms, functioning, history, context, and other possible causes.

What the score cannot tell you

Neither result is conclusive. A high total does not identify which condition, if any, is present, while a low total does not prove that a person has no mental health condition.

The developer notes that symptom screens can miss people whose symptoms are controlled by treatment.

The score is best read as one measure of recent distress. It should not decide treatment, urgency, or eligibility for services by itself.

Evidence and limitations

The original development study compared K6 scores with cases identified through structured diagnostic interviews. That evidence is about screening performance, not diagnosis. Later cross-population research found that useful calibration depends on population and purpose.

That evidence does not make the K6 a disorder-specific test. Language, population, administration method, timeframe, and missing-data rules can all affect interpretation.

The 13-or-more boundary supports a defined U.S. surveillance method. It is not a universal clinical severity band.