Performance of the 6-item Kessler scale for measuring serious mental illness in Hong Kong

BackgroundThe 6-item Kessler scale (K6) promises to be a valuable epidemiological tool for assessing serious mental illness (SMI) in communities with limited resources for psychiatric research and treatment. Its performance in Chinese community has not been studied with reference to clinically assessed SMI.MethodFrom a representative telephone-based population survey (n = 3014) that administered the K6, 153 participants were readministered the K6 and, on the same day, interviewed face-to-face by clinicians using the Structured Clinical Interview for Diagnostic and Statistical Manual of Mental Disorder, Fourth Edition, Axis I Disorder. Predictive indicators such as McNemar χ², area under receiver operating characteristic curve and stratum-specific likelihood ratios were used to investigate the concordance between the K6 and clinical status of SMI, individual-level predicted probabilities of having SMI, and the weighted prevalence of SMI in the community.ResultThe K6 exhibited high internal consistency and test-retest reliability. Factor analysis revealed 2 correlating components composed of depression and anxiety. Matching of K6 caseness and SMI status showed that at the cutoff of 12/13, the area under receiver operating characteristic curve was moderate (0.69). The K6 had high specificity and was a stronger screen-out than screen-in tool for SMI. The weighted prevalence estimate of SMI in Hong Kong was 6.5%. A person scoring 13 or above on the K6 has a probability of at least 22.2% of having SMI.ConclusionThe Chinese K6 is reliable and generates the likelihood of SMI with substantial concordance with face-to-face clinical interviews in Hong Kong. It is a valuable tool for screening SMI, behavioral risk factor surveillance, and community epidemiological surveys.