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

TLDR

The IQCODE is an informant‑report questionnaire that captures changes in an elderly person's everyday cognitive function. It was designed to assess cognitive decline independently of pre‑morbid ability. The study administered the IQCODE to 613 informants from the general population and to informants of 309 dementia patients who had completed it a year earlier. Principal component analysis confirmed a single cognitive‑decline factor, the questionnaire showed excellent internal consistency (α = 0.95), good one‑year test‑retest reliability (r = 0.75), discriminated well between general and dementia samples, and had a negligible correlation with education (r = –0.13).

Abstract

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.