Cognitive impairment was assessed using the Chinese version of the Mini-Mental State Examination (MMSE) which was validated against psychiatrist diagnosis in the elderly Hong Kong population (Katzman et al., 1988). MMSE scores ranged from 0 to 30. The lower the MMSE score was, the more severe dementia-related cognitive impairment was. A subject with a score below 24 points at follow up was identified as demented (Tombaugh and McIntyre, 1992), they were excluded in the analysis in order to assess depressive symptoms reliably.