  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: 3,571 individuals (67.1 {\pm} 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
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 ({\Delta}R2 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.
