Quality of measurement instruments assessing Planetary and One Health Literacy related constructs: a systematic review

Abstract Background Amid accelerating anthropogenic climate and ecological crises, the expansion of health literacy as a comprehensive and multidimensional concept addressing upstream determinants of health has become relevant. A critical gap persists in measurement research to identify validated instruments for health literacy within the environment-health nexus. Objective To conduct a systematic review of the quality of existing instruments that measure Planetary and One Health Literacy or related constructs according to the COnsensus-based Standards for the selection of health Measurement INstruments (COSMIN) methodology. Methods A systematic literature search was performed in Medline, Embase, Web of Science, CINAHL, APA PsychInfo, APA PsycArticles, PSYNDEX, and Greenline to identify development and/or validation studies of suitable instruments. We assessed the risk of bias of each study, systematically evaluated the psychometric properties of instruments, and graded the certainty of evidence to inform recommendations for instrument use and further development. Results Out of 192 screened records, we identified four studies employing three instruments: Climate Change Health Literacy Scale (CCHLS), Climate Change and Infectious Disease Literacy Scale, and Sustainable Food Literacy Scale (SFLS). The quality of evidence for the development and content validity in all instruments was rated low or very low. Of all scales the SFLS demonstrated the best results in the assessed measurement properties supported by very good quality of evidence in its original, while its Turkish adaptation had low methodological quality in its assessed measurement properties and insufficient reliability. Conclusion The included studies emphasised quantitative validation over robust instrument development and transparency in their reporting, highlighting the need for clearly defining constructs and involving target populations in the design processes. While existing measurement instruments primarily assess knowledge, attitudes, and behaviour, the lack of attention to the health literacy’s construct calls for stronger integration between health literacy, Planetary Health, and One Health research.