The European Psychiatric Services: Inputs Linked to Outcome Domains and Needs (EPSILON) Study aims to produce standardised versions in five European languages of instruments measuring needs for care, family or caregiving burden, satisfaction with services, quality of life, and sociodemographic and service receipt.
To describe background, rationale and design of the reliability study, focusing on reliable instruments, reliability testing theory, a general reliability testing procedure and sample size requirements.
A strict protocol was developed, consisting of definitions of the specific reliability measures used, the statistical methods used to assess these reliability coefficients, the development of statistical programmes to make inter-centre reliability comparisons, criteria for good reliability, and a general format for the reliability analysis.
The reliability analyses are based on classical test theory. Reliability measures used are Cronbach's α, Cohen's κ and the intraclass correlation coefficient. Intersite comparisons were extended with a comparison of the standard error of measurement. Criteria for good reliability may need to be adapted for this type of study. The consequences of low reliability, and reliability differing between sites, must be considered before pooling data.