The validity and reliability of diagnoses of work-related mental ill-health

OBJECTIVES: To establish the reliability and validity of work-related mental ill-health diagnoses. BACKGROUND: A UK-based surveillance scheme for work-related ill-health involving occupational physicians (OPs) reporting suggests that mental ill-health incidence is increasing by around 13% per year, with anxiety, depression and "other work-related stress" being the most common diagnoses. There have been no studies of the validity and reliability of such diagnoses. Given the existence of a large network of psychiatrists (PSYs) also involved in surveillance of work-related ill-health, an opportunity arose to measure the concurrent validity and reliability of work-related mental ill-health diagnoses. METHODS: 100 anonymised summaries of cases previously reported by OPs or PSYs were collected; each was sent to 5 PSYs and 5 OPs, who assigned a diagnosis and judged whether the case was work-related. Concurrent validity of the ill-health aspect of the diagnoses, and of the opinion as to work-relatedness, was assessed by comparing the overall classifications of cases by OPs and PSYs. Reliability of the diagnostic classification was measured by kappa matrices. RESULTS: Diagnostic proportions for PSYs and OPs demonstrated good agreement for anxiety, depression, anxiety plus depression and "stress" (11%, 34%, 27%, 14%) and (14%, 30%, 27%, 17%), respectively. In both groups, kappa coefficients were high for a psychotic diagnosis (0.78, 95% CI: 0.74 to 0.83), but not as high for anxiety (0.27, 95% CI: 0.23 to 0.32), depression (0.34, 95% CI: 0.29 to 0.38) and "stress" (0.15, 95% CI: 0.10 to 0.19). The odds ratio of classifying a case as work-related among PSYs compared to OPs was 2.39 (95% CI: 1.68 to 3.38), p<0.001. CONCLUSIONS: The overall agreement between OPs and PSYs on mental ill-health diagnoses suggests that OP diagnoses are valid for epidemiological purposes. However, the within-group reliability of the diagnosis "stress" is low. Given differences in judgements about work-relatedness, further research is needed to investigate this aspect of a diagnosis.