The Informant Questionnaire on Cognitive Decline in the Elderly (IQCODE): socio-demographic correlates, reliability, validity and some norms.

The IQCODE is a questionnaire which asks an informant about changes in an elderly person's everyday cognitive function. The questionnaire aims to assess cognitive decline independent of pre-morbid ability. In the present study, the IQCODE was administered to a sample of 613 informants from the general population. In addition, the questionnaire was administered to informants of 309 dementing subjects who had filled it out one year previously. A principal components analysis, using the general population sample, confirmed that the IQCODE measures a general factor of cognitive decline. The questionnaire was found to have high internal reliability in the general population sample (alpha = 0.95) and reasonably high test-retest reliability over one year in the dementing sample (r = 0.75). The total IQCODE score, as well as each of the 26-items, was found to discriminate well between the general population and dementing samples. The correlation with education was quite small (r = -0.13), indicating that contamination by premorbid ability is not a problem.