Purpose: Using the reliable and clinically significant change approach, we aimed to identify meaningful outcome indicators for the Health of the Nation Outcome Scales (HoNOS) and to combine them in a single model. We applied these indicators to the 1-year outcome of two large samples of people attending community mental health services in Italy (cohort 1) and the Netherlands (cohort 2).
Methods: Data were drawn from two studies on routine outcome assessment. The criteria for meaningful outcome were defined on both study cohorts and both language versions of the scale. The model combined (a) two criteria for adequate change (at least 4 or 8 points change), (b) two cut-offs for clinically significant change (a total score of 10 was the threshold between mild and moderate illness, 13 between moderate and severe illness), and (c) a method for classifying stable subjects in three degrees of severity (stable in mild, moderate or severe illness). Results were compared with those given by the effect size (ES) and analysis of variance and covariance (ANOVA and ANCOVA).
Results: For the proposed approach the outcome of cohort 1 was better than cohort 2, with 65-67% of its subjects showing a positive outcome compared to only 45-46%. The other reference methods (ES and ANOVA), however, showed a greater improvement for cohort 2. ANCOVA indicated that the differences were due to regression to the mean (RTM) which showed opposite effects across the two cohorts.
Conclusions: The proposed approach proved valuable and generalizable for interpreting outcome on HoNOS, scarcely influenced by the RTM effect. Its introduction could benefit outcome evaluation and management.