The Informant Questionnaire on Cognitive Decline in the Elderly (IQCODE): a review

The IQCODE is widely used as a screening test for dementia, particularly where the subject is unable to undergo direct cognitive testing or for screening in populations with low levels of education and literacy. This review draws together research on the psychometric properties and validity of the IQCODE.A systematic search of the literature was carried out using three databases.The review shows that the questionnaire has high reliability and measures a single general factor of cognitive decline. It validly reflects past cognitive decline, performs at least as well at screening as conventional cognitive screening tests, predicts incident dementia, and correlates with a wide range of cognitive tests. A particular strength is that the IQCODE is relatively unaffected by education and pre-morbid ability or by proficiency in the culture's dominant language. The disadvantage of the IQCODE is that it is affected by informant characteristics such as depression and anxiety in the informant and the quality of the relationship between the informant and the subject.Because the IQCODE provides information complementary to brief cognitive tests, harnessing them together can improve screening accuracy.