Measuring the mental health status of the Norwegian population: a comparison of the instruments SCL-25, SCL-10, SCL-5 and MHI-5 (SF-36).

A great number of questionnaires and instruments have been developed in order to measure psychological distress/mental health problems in populations. The Survey of Level of Living in 1998 conducted by Statistics Norway used both Hopkins Symptom Checklist (SCL-25) and the Short Form 36 (SF-36), including the five-item mental health index (MHI-5). Five-item and 10-item versions of the SCL-25 have also been used in Norwegian surveys. The purpose of this study was to investigate the correlation between the various instruments, and to assess and to compare psychometric characteristics. A random sample of 9735 subjects over 15 years of age drawn from the Norwegian population received a questionnaire about their health containing SCL-25 and SF-36. Response rate was 71.9%. Reliability of the SCLs and MHI-5 were assessed by Cronbach alpha. The scores from full and abbreviated instruments were compared regarding possible instrument-specific effects of gender, age and level of education. The correlations between the instruments were calculated. The capacity of the various instruments to identify cases was assessed in terms of sensitivity, specificity, predictive values, receiver operating characteristics (ROC) and area under the curve (AUC). The reliabilities were high (Cronbach alpha>0.8). All instruments showed a significant difference in the mean scores for men and women. The correlation between the various versions of SCL ranged from 0.91 to 0.97. The correlation between the MHI-5 and the SCLs ranged from -0.76 to -0.78. The prevalence rate was 11.1% for SCL-25 scores above 1.75 and 9.7% for scores below 56 in MHI-5. AUC values indicated good screening accordance between the measures (AUC>0.92). The results suggest that the shorter versions of SCL perform almost as well as the full version. The corresponding cut-off points to the conventional 1.75 for SCL-25 are 1.85 for SCL-10 and 2.0 for SCL-5. MHI-5 correlates highly with the SCL and the AUC indicate that the instruments might replace each other in population surveys, at least when considering depression. An operational advantage of the MHI-5 over the SCL instruments is that it has been widely used not only in surveys of mental health, but also in surveys of general health.