Self-reports on the IQCODE in older adults: a psychometric evaluation.

The Informant Questionnaire on Cognitive Decline (IQCODE) has been successful in identifying demented persons in a general population. In this study, this questionnaire was used as a self-report screening for dementia symptoms. The object was to investigate the feasibility, homogeneity, and construct validity of self-reports on the IQCODE. Participants were 4823 community-dwelling older adults who received an IQCODE-SR. Feasibility was assessed on the basis of response rate, the proportion of missing data for each item, and the number of persons who received help in completing the questionnaire. Homogeneity was checked with Cronbach's alpha. To investigate construct validity, hypotheses on performance of the IQCODE-SR were tested. Feasibility was acceptable, with a response rate of 58.9%. Missing answers per item ranged from 2.5% to 7.3%, and 915 of 2841 participants received help in completing the questionnaire. Homogeneity was good, with Cronbach's alpha = .94. The majority of hypotheses on construct validity were confirmed. It was concluded that the IQCODE-SR meets the basic requirements of a good measurement instrument.