Mapping the evidence on the Patient Health Questionnaire-9 (PHQ-9): a living systematic review of studies on measurement properties

Background

The WHODAS 2.0 is a widely used patient-reported outcome measure (PROM) of functional disability, with the WHODAS-12 as its most commonly used short form. As its use expands across diverse populations, clinical contexts, and languages, it is important to establish whether its measurement properties are consistent across settings. A broad overview of the existing evidence is therefore needed to assess the strength and coverage of the evidence and identify remaining gaps.

Aims

We aim to map and characterise studies reporting on the measurement properties of the WHODAS-12, including their populations, settings, versions of the instrument, and measurement properties assessed. This review forms part of a broader living evidence infrastructure comprising parallel systematic reviews and an open-access platform covering four PROMs recommended by the Common Measures in Mental Health Science Initiative: the PHQ-9, GAD-7, WHODAS 2.0, and RCADS-25.

Methods

A systematic search was conducted in five major bibliographic databases up to January 2026. Titles, abstracts, and full texts were screened independently in pairs, with disagreements resolved by consensus or a third reviewer. Eligible studies are peer-reviewed empirical reports evaluating at least one measurement property of the WHODAS-12 across any population, setting, or study design. Data extraction and synthesis follow two phases. In Phase A (mapping), pairs of researchers extracted data on study and sample characteristics, WHODAS-12 version, and measurement properties assessed, classified according to the COnsensus-based Standards for the selection of health Measurement INstruments (COSMIN) taxonomy, to systematically map and characterise the available evidence. In Phase B (synthesis; not presented here), risk of bias will be rated using the COSMIN Risk of Bias checklist, and narrative and quantitative evidence syntheses will be conducted within homogeneous subgroups of studies.

Results

Phase A mapping of the WHODAS-12 literature was completed for 82 articles examining 117 samples or substudies. The WHODAS-12 was more often interviewer-administered (56%) than self-reported (33%). Studies were conducted across 46 countries, most commonly in Europe and the Americas. Sample sizes ranged from 17 to 23,757, with an average of 55% female participants. Populations were most often recruited for physical (51%) or mental (33%) health conditions, and lived experience involvement in the conduct of the studies was rarely reported (3%). Internal consistency and structural validity were the most frequently assessed measurement properties (62% each). Among studies in populations with mental health conditions (39 samples reported in 25 articles), depression, anxiety, and psychotic disorders were the most commonly represented, with structural validity and hypothesis testing most frequently examined (62% each).

Conclusions

The WHODAS-12 evidence base spans diverse populations, languages, and settings, but coverage of measurement properties is uneven. Among mental health populations, evidence is concentrated in a small number of diagnostic groups and properties. Identifying these gaps supports more context-sensitive selection of the instrument and highlights priorities for future validation work. Findings will feed into a living, open-access platform allowing users to browse and filter measurement-property evidence across all four PROMs.

References

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