Home / Resources / Psychological Measures / K6
Kessler Psychological Distress Scale (K6):
Scoring and the Cut-off of 13
The Kessler Psychological Distress Scale (K6) is a six-item measure of nonspecific psychological distress over the past 30 days, summed to a total of 0 to 24 when items are coded 0 to 4 (Kessler et al., 2002). K6 scoring is simple until a dataset stores 1 to 5 instead. Converting those codes comes first here, followed by the serious-distress flag at 13 or more, why that flag is not a diagnosis, and the same two steps written in SPSS and in R.
What the K6 Measures
The K6 summarizes nonspecific psychological distress experienced during the preceding 30 days, including symptoms associated with anxiety and depressed mood. Kessler and colleagues (2002) developed the K6 and the longer K10 as brief indicators suitable for monitoring population mental-health trends.
In the United States, the K6 is used in large surveys including the National Health Interview Survey and in epidemiologic research. It helps identify likely serious psychological distress, but it does not separate individual diagnostic categories and should not be treated as a substitute for a structured mental-health assessment.
Structure of the K6
- Items: six self-reported symptom frequency responses.
- Response scale: conventionally recoded to 0 to 4, from none to all of the time, referring to the past 30 days. Some datasets store 1 to 5 instead, and response labels and ordering vary across implementations.
- Subscales: none. Standard K6 has no reversed items, supplementary subtotal or formal subscale.
- Total: one score from 0 to 24 with the conventional US response scoring. A valid score requires consistent recoding of all six item response categories.
- Versions: the longer K10 is a distinct instrument, not a substitute for absent K6 items.
- Translations: cross-cultural and multilingual K6 forms are in use in US population surveillance.
The instrument itself is available from the Harvard National Comorbidity Survey K6/K10 scales page and US health-survey documentation.
How to Score the K6
- Check that k1 to k6 are coded 0 to 4 (higher always means more frequent distress). If they are stored as 1 to 5, subtract one from each scored item before summing.
- Sum the six items to form k6_total, which ranges from 0 to 24.
- Define k6_high as 1 for a score of 13 or more and 0 otherwise, if using the US serious psychological distress screening threshold.
- The sample code uses complete-case scoring: any missing item yields a missing total. Do not substitute a zero for a missing response without a prespecified, justified rule.
* Illustrative syntax: variables must already be valid item scores (0 to 4).
COMPUTE k6_total=SUM.6(k1 TO k6).
IF (NOT MISSING(k6_total)) k6_high=(k6_total>=13).
EXECUTE.# data: one row per respondent; items k1 to k6 coded 0 to 4.
data$k6_total <- rowSums(data[paste0("k",1:6)],na.rm=FALSE)
data$k6_high <- ifelse(is.na(data$k6_total),NA,data$k6_total>=13)Interpreting K6 Scores
| Score band | Interpretation |
|---|---|
| 0 to 12 | Below the conventional 13 or more serious-distress screening threshold |
| 13 to 24 | At or above the high-distress screening threshold |
| 0 to 24 | Continuous distress severity metric |
Source: Kessler et al. (2002, 2003).
Greater totals represent more frequent psychological distress over the preceding month. A threshold of 13 or more was calibrated against clinical interview data in the NCS-R to identify serious mental illness (Kessler et al., 2003) and is used in US population surveillance, but predictive performance may change with the prevalence and composition of the sample. A lower range of 5 to 12 has been proposed as moderate distress (Prochaska et al., 2012); label any such band explicitly.
Distinguish a K6 screening classification from a DSM diagnosis. If the database stores categories 1 to 5, the naive sum has a range of 6 to 30; convert it first before applying the threshold of 13.
Psychometric Properties
| Property | Published finding | Source |
|---|---|---|
| Internal consistency | The original work reports K6 α approximately .89 | Kessler et al. (2002) |
| Construct validity | Designed to monitor nonspecific psychological distress in population studies, including the high-severity tail | Kessler et al. (2002) |
| US measurement context | Used in large national health surveys including NHIS and NSDUH | Kessler et al. (2003) |
| Cross-cultural equivalence | Measurement-invariance studies indicate language and population differences warrant explicit examination | Cross-cultural measurement-invariance research |
| Diagnostic performance | A score of 13 or more identified serious mental illness in the NCS-R calibration (AUC ≈ .86); not a disorder-specific diagnostic algorithm | Kessler et al. (2003) |
These are source-specific results and cannot be assumed to hold as reliability or accuracy estimates in a new sample.
Using the K6 in a Study
Model the K6 as a continuous distress outcome when the scientific question is symptom burden, for instance with a Multiple Linear Regression, and as a binary indicator of 13 or more when estimating the prevalence of serious psychological distress, where Incidence & Prevalence Analysis applies and Logistic Regression models the predictors. In complex US surveys, incorporate sampling weights, strata and clusters where supplied, rather than treating survey data as a simple random sample.
Because the threshold of 13 was developed as a population screening index, document population and measurement differences when using it in university cohorts or clinical samples. Report sample reliability (alpha or omega) through Reliability Analysis (Cronbach’s Alpha), together with item missingness and appropriate uncertainty intervals. No universal K6 minimal clinically important difference is established in Kessler et al. (2002).
Related field: Public Health
Reporting the K6
Nonspecific psychological distress was assessed with the six-item Kessler Psychological Distress Scale (K6; Kessler et al., 2002). Items referring to the preceding 30 days were coded 0 to 4 and summed (range = 0 to 24); higher totals indicated more distress. A binary high-distress indicator was defined as K6 ≥ 13. Internal consistency was [α = XX], and missing values were managed using [method].
References
Harvard Medical School. (n.d.). K10 and K6 scales. https://www.hcp.med.harvard.edu/ncs/k6_scales.php
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. https://doi.org/10.1017/S0033291702006074
Kessler, R. C., Barker, P. R., Colpe, L. J., Epstein, J. F., Gfroerer, J. C., Hiripi, E., Howes, M. J., Normand, S.-L. T., Manderscheid, R. W., Walters, E. E., & Zaslavsky, A. M. (2003). Screening for serious mental illness in the general population. Archives of General Psychiatry, 60(2), 184-189. https://doi.org/10.1001/archpsyc.60.2.184
Prochaska, J. J., Sung, H.-Y., Max, W., Shi, Y., & Ong, M. (2012). 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, 21(2), 88-97. https://doi.org/10.1002/mpr.1349
Frequently Asked Questions
What is the standard K6 score range?
Zero to 24 when all six responses have been converted to 0 to 4.
Is a K6 score of 13 a psychiatric diagnosis?
No. A score of 13 or more is a conventional population screening threshold for serious distress.
What if my dataset uses 1 to 5 response codes?
Subtract one from each of the six coded items, check the category order, and then sum.
Is the K6 the same as the K10?
No. The K10 is the longer, ten-item version and has a different score range.
NEXT STEP
Need K6 Totals and
Cut-off Flags Checked?
OnlineSPSS is a statistical consultancy for researchers. Share your design and dataset, and a statistically trained Research Coordinator reviews it. The scope and one fixed project fee are confirmed before work begins.
No Commitment Required
Strictly Confidential
Fixed Project Fee
In-House PhD-Level Statisticians
Same-Day Response
Serving Researchers Since 2014