Background: Lifetime rates of depression reported in epidemiological surveys are generally only twice the 12 month rates. Either people forget the symptoms of depression or many people who have a depressive episode remain depressed for many years. Both may be true. There is a need to examine the long-term clinical validity of interviews that are used to make lifetime diagnoses.
Methods: Forty-five patients who were part of a long-term follow-up study of depression were interviewed 25 years after the index episode. The diagnoses from the original, fully structured interviews were compared with the responses people made for that period when interviewed using the CIDI 25 years later.
Results: Twenty-seven patients met CIDI DSM-III-R criteria for depression at index episode. At the 25 year follow-up, 19 of the 27 reported the essential symptoms of 'depression or loss of interest' being present at the index time, and in 14 of the 27 the depressive symptoms recalled met criteria for DSM-III-R major depressive episode at that time.
Conclusions: Seventy per cent of people who were hospitalized for a major depressive episode can recall being depressed but only half can recall sufficient detail to satisfy the diagnostic criteria when interviewed 25 years later. As depressive episodes, especially those severe enough to warrant admission, are recalled better than many other diagnoses, one must be cautious about the lifetime rates for mental disorders reported in retrospective epidemiological surveys.