Sensitivity of the informant questionnaire on cognitive decline: an application of item response theory

The Informant Questionnaire on Cognitive Decline (IQCODE) is a formal informant report instrument, originally developed by Jorm and Jacomb (1989; Psychological Medicine, 19(4), 1015). The goal of the present study was to evaluate the range of cognitive decline in which the IQCODE is most sensitive, using item response theory (IRT). Existing data (N = 740) from a sample of community-dwelling older adults was used for this purpose. A 2-parameter model estimating item difficulty and discrimination fit the data best. Additionally, the IQCODE provided the most psychometric information in the range of -0.5 < theta < 1.5, with peak information obtained at approximately theta = 0.4. Based on individuals' latent score (theta) estimates, items on the IQCODE are adequate for use as a screening tool for dementia. Results of the item calibration may be useful for targeted assessment needs, such as the development of short forms.