The validity of instruments to measure knowledge in population-based cancer screening targeting individuals at average risk - A systematic review

Objectives: Relevant knowledge is essential for informed choices about (non)participation in population-based cancer screening. Many instruments have been proposed to assess residents' knowledge about cancer screening programmes but their measurement properties are unknown. This systematic review aims to identify and critically evaluate the measurement properties of instruments to measure knowledge about cancer screening in individuals eligible for population-based screening. Methods: A literature search was undertaken in PubMed, PsycINFO, Embase, CINAHL, Scopus and Web of Science in August 2023. The review included any study reporting one or more measurement properties of the questionnaire or sub-scale used measuring knowledge of cancer screening including breast, colorectal and/or cervical cancer screening. Studies including males aged 45 or older and females aged 20 or older were included. Two independent reviewers screened the articles and assessed the included articles using the COnsensus-based Standards for the selection of health Measurement Instruments (COSMIN). Results: We included 24 instruments, which varied in number and characteristics of items. All instruments were assessed as having an inadequate instrument development. The results of structural validity, internal consistency, criterion validity and reliability were assessed as indeterminate, while construct validity and responsiveness were assessed as sufficient. Conclusion: This systematic review identified no instruments to measure knowledge about cancer screening where the measurement properties were sufficiently evaluated. There is a lack of focus on content validity and structural validity, and further validation of the instruments is needed. The results indicate a lack of shared understanding or agreement of what constitutes relevant knowledge about cancer screening.