Background: Data is usually collected from different sources in family studies in depression. We sought to determine what effect different methods of data collection had on the reporting of the lifetime prevalence of depression in the relatives of depressed probands.
Method: We examined the psychiatric histories of 519 first-degree relatives of a consecutive series of 89 hospitalised depressed probands to ascertain their lifetime prevalence of RDC Major Depression. These data on relatives were obtained either directly with the SADS-L (n = 116), indirectly with the Family History RDC (FH-RDC) (n = 283) or by examining the casenotes of the probands (n = 120).
Results: The method of data collection had a marked effect on the reported prevalence of depression, with direct interview being much more sensitive in detecting the less severe forms of the illness. The lifetime prevalence of hospitalised depression in relatives, however, was unaffected by the method of the data collection. Variation in lifetime prevalence of depression between the SADS-L and FH-RDC appeared to be due mainly to differences in the sensitivity of the instrumentation rather than to biases in sampling.
Conclusion: We confirm that indirect sources of family information have reduced sensitivity for the detection of depression in relatives compared with direct interview.
Limitations: The numbers of relatives directly interviewed were small and the probands represented a severely affected sample which limits the generalisability of the findings.
Clinical relevance: Combining data from different methods of collection in family studies is therefore problematic unless a narrow definition of caseness is used (e.g. depression requiring hospitalisation).