The influence of diversity on the measurement of functional impairment : an international validation of the Amsterdam IADL Questionnaire in eight countries
Introduction: To understand the potential influence of diversity on the measurement of functional impairment in dementia, we aimed to investigate possible bias caused by age, gender, education, and cultural differences. Methods: A total of 3571 individuals (67.1 ± 9.5 years old, 44.7% female) from The Netherlands, Spain, France, United States, United Kingdom, Greece, Serbia, and Finland were included. Functional impairment was measured using the Amsterdam Instrumental Activities of Daily Living (IADL) Questionnaire. Item bias was assessed using differential item functioning (DIF) analysis. Results: There were some differences in activity endorsement. A few items showed statistically significant DIF. However, there was no evidence of meaningful item bias: Effect sizes were low (ΔR2 range 0-0.03). Impact on total scores was minimal. Discussion: The results imply a limited bias for age, gender, education, and culture in the measurement of functional impairment. This study provides an important step in recognizing the potential influence of diversity on primary outcomes in dementia research ; The development of the Amsterdam IADL Questionnaire is supported by grants from Stichting VUmc Fonds and Innovatiefonds Zorgverzekeraars. The Amsterdam Alzheimer Center is supported by Stichting Alzheimer Nederland and Stichting VUmc Fonds. The present study is supported by a grant from Memorabel (733050205), which is the research program of the Dutch Deltaplan for Dementia. The chair of WMF is supported by the Pasman stichting. The clinical database structure for the Amsterdam Dementia Cohort was developed with funding from Stichting Dioraphte. DF, CLB and AXPR are supported by FEDER grant PSI2014-55316-C3-1-R, the Spanish National Research Agency grant PSI2017-89389-C2-1-R and the Galician Government GI-1807-USC: Ref. ED431-2017/27. GSB, JLM and the ALFA+ project has received funding from "la Caixa" Foundation (ID 100010434), under agreement LCF/PR/GN17/50300004 and the Alzheimer's Association and an international anonymous ...