Development and content validity of the cognition in daily life scale (CDL).

Cognitive impairment can negatively influence daily functioning. Current cognitive measures are essential for diagnosing cognitive impairment, but findings on these tests do not always represent the level of cognitive functioning in daily life. Therefore, this study aimed to design a structured measurement instrument to observe and rate the impact of cognitive impairment in daily life, named the cognition in daily life scale for persons with cognitive problems (CDL). In this paper we describe the development, expected usability, and psychometric properties (content and face validity) of the instrument. The CDL was established through three consecutive development phases: (1) item selection, (2) item categorization and comparison, and (3) item revision and manual construction. Subsequently, a panel of eleven international experts rated the relevance of the selected items and provided comments on the expected usability and face validity. Content validity was estimated with the content validity index, based on which four items were removed. The experts' comments led to minor adjustments of the manual, domains, and formulation of the maintained items. The final instrument consists of 65 items describing behaviour that relies on cognitive functions within six domains. Future research should focus on evaluating the construct validity and reliability of the CDL.