K6: Kessler Psychological Distress Scale, 6-item version

What this assessment is

The K6 is brief by design. Its six items record how often a person experienced several forms of emotional distress during the past 30 days.

It is a screen.

Ronald Kessler and colleagues developed it as the short form of the 10-item K10. The six K6 questions are part of the K10 rather than a separate set of questions.

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. Its main purpose was to help estimate serious mental illness in the general adult population with few questions.

The purpose was narrow.

Researchers also use it to compare distress across groups and over time, but useful comparisons require the same version, timeframe, and scoring method.

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.

Timeframe changes matter. A seven-day result should not be compared directly with a 30-day result without evidence that supports that comparison.

What it measures

The K6 covers a broad cluster of distress linked with anxiety and depression. The distinction matters: it measures frequency, not the cause of the feelings or the diagnosis behind them.

The 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

Two common coding systems are used:

• 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 difference is mechanical. The same response pattern is six points higher under the Australian method, so the two totals should never be treated as interchangeable.

Do not mix them.

The official scoring guide describes both systems. A report should always state which range it uses.

Completeness matters too. The developer does not prescribe one universal missing-response method. The U.S. National Center for Health Statistics calculates a total only when all six responses are present.

How to interpret a K6 score

A cutoff is not a verdict.

For the 0 to 24 method, U.S. population studies often use 13 or more to classify serious psychological distress. The equivalent boundary is 19 or more with the 6 to 30 method.

Context matters.

The developer explains that 13 or more was calibrated for prevalence estimates in the total U.S. population. Its accuracy changes when a population has a different prevalence of serious mental illness.

The population matters. The National Center for Health Statistics uses 13 or more in reports about U.S. adults. That reporting rule does not turn an individual result into a diagnosis.

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

What the score cannot tell you

A number needs context.

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

Low does not mean absent.

Current treatment can also lower distress while a condition remains part of the person's history. The developer notes that brief symptom scales can miss people whose symptoms are well controlled.

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 K6 was built for efficient population screening. The original research found that it could separate likely serious mental illness cases from non-cases in the studied samples.

Breadth is the tradeoff.

That evidence does not make the K6 a disorder-specific test. Results can also change with language, population, administration method, timeframe, and missing-data rules.

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