Measurement equivalence of the SRQ-20 across armed-conflict exposure, sex, and region in Colombia (ENSM 2015)

Background. The SRQ-20 screens common mental distress in low- and middle-income countries, yet its equivalence across groups, especially armed-conflict exposure, is rarely tested with methods that separate true invariance from an underpowered null. We evaluated its psychometric properties and measurement equivalence in Colombian adults. Methods. In 10,865 adults from the 2015 Colombian National Mental Health Survey, we assessed dimensionality, fitted a two-parameter logistic (2PL) model, and tested equivalence across armed-conflict exposure, sex, and region using multiple-group models with purified anchoring and freely estimated group means, separating true distress differences from item bias. Item functioning was equivalence-tested against a {+/-} 0.10 band on signed expected-score differences (SIDS), with test-level differential test functioning (DTF) plus severity-graded and design-weighted sensitivity analyses. Criterion validity used design-weighted ROC against 12-month CIDI diagnoses. Results. The scale was essentially unidimensional (one-factor CFI = .945, rising to .971 with four content-redundant item pairs modelled; explained common variance = .71) and fit the 2PL well, with high conditional reliability at the cut-points (.93-.94). Once true distress differences were separated from item bias, the SRQ-20 was equivalent across armed conflict exposure (all |SIDS| < .10, maximum .03; net DTF {approx} 0.1 points) and region, holding even among directly victimised adults; sex was partially invariant (three items; DTF {approx} 0.85 points). Design-weighted AUC was .88 (major depression) and .84 (any disorder). Conclusions. The SRQ-20 measures distress equivalently across armed-conflict exposure (including direct victimisation) and region in Colombian adults, supporting exposed-non-exposed comparisons within this population; raw-total sex comparisons carry a small, quantifiable bias. The 20-item form is recommended.