Subject and informant variables affecting family history diagnoses of depression and dementia.

The aim of the present study was to evaluate subject and informant factors affecting the validity of the family history for dementia and depression. Relatives of patients and control subjects (n = 531) were interviewed directly. At least one 'significant' other provided family history information on every interviewed relative. The detection of dementia or depression based on the family history increased with the severity of the respective disorder. The likelihood of detecting dementia based on the family history increased in proportion to the subject's age. A lifetime diagnosis of depression in the informant improved the detection of this disorder in a relative. The presence of another psychiatric disorder in either the interviewed relative or the informant significantly increased the risk for false-positive diagnoses of depression. The present results demonstrate that family history information on depression and dementia is influenced by different proband and informant variables. On the basis of these results, we cannot recommend reducing thresholds for family history diagnoses.