How Many Instruments Do We Need? Strengths, Weaknesses, and Potentials for Further Developments of Digital Health Literacy Measurement Instruments: Narrative Overview of Reviews and Content Analysis.

Background: With the ongoing digitalization of health care, digital health literacy (DHL) is becoming increasingly important, requiring appropriate measurement instruments (DHLMIs). However, the wide range of available DHLMIs makes selection difficult and raises questions about their suitability and comparability. Objective: This review aimed to provide an overview of available DHLMIs for adult populations and to compare their dimensions, identifying overlaps and differences to determine which (key) dimensions are most commonly studied and thus define DHL. Methods: A narrative overview of reviews was conducted. The database search was conducted in November 2024, with an updated search in March 2026, in PubMed and Google Scholar using specific search terms and predefined inclusion and exclusion criteria. This was complemented by a forward citation search in Web of Science. All identified records were screened in a multistage process. At the review level, systematic and scoping reviews published since January 1, 2020, were included that analyzed DHLMIs in adult populations. At the primary study level, studies were included in which DHLMIs were used for self-assessment, performance-based evaluation, or a combination of both. Data extraction was performed by one reviewer and verified by a second reviewer. Data on underlying theories, methods of data collection (performance-based or self-reported), and target groups were extracted. DHL dimensions, their definitions, and the associated items were categorized by 2 researchers using qualitative content analysis according to Kuckartz. Results: A total of 12 reviews were included. Of the 170 measurement instruments examined in these reviews, 33 (19%) were selected for detailed analysis after applying the inclusion and exclusion criteria. The majority of the included measurement instruments (n=20, 61%) were not based on a theory, 20 (61%) measured DHL exclusively via self-report, and 21 (64%) addressed specific target groups. The measurement instruments encompassed a total of 209 original dimensions of DHL. The number of dimensions measured per instrument varied between 2 and 22. The qualitative content analysis identified a total of 30 assigned dimensions. Key dimensions captured in almost all instruments, although under different names, include evaluating health information, using health information, researching health information, and the ability to use technology. Conclusions: The large number of measurement instruments and original dimensions makes it difficult to select suitable instruments for measuring DHL and to compare and synthesize study results. Nevertheless, we were able to identify key dimensions as relevant regardless of target groups and types of digital applications, which could be used to develop a core outcome set for DHL. Our findings offer a foundation for refining existing instruments and developing new ones. They provide practical guidance for researchers and health care professionals in selecting suitable DHLMIs. Additionally, our review underlines the importance of theory to ensure content validity and comparability of DHLMIs.