Measuring the influence of commercial determinants of health at the individual level: Protocol for tool development and validation.

INTRODUCTION: Existing frameworks on Commercial Determinants of Health (CDoH) largely focus on macro-level corporate practices and policy environments. Individual-level exposure-mediated through targeted marketing, pricing strategies, product availability and placement-remains underexplored, particularly in low- and middle-income countries. The absence of standardised tools to capture these exposures limits the ability to quantify commercial influences on health and weakens evidence-informed public health responses. There is a critical need for a robust, contextually grounded instrument to measure individual-level exposure to CDoH. Developing and validating an individual-level CDoH measurement tool is therefore essential to strengthen research, surveillance and policy action aimed at mitigating health-harming commercial influences. The availability of this tool will allow policymakers and public health practitioners to identify high-risk populations and monitor the effectiveness of regulatory actions addressing harmful commercial practices.

METHODS AND ANALYSIS: This study will follow standard guidelines for tool (questionnaire) development. The process will include four sequential phases: item generation, refinement, validity testing and construct validation. A literature review with a systematic search strategy and in-depth interviews with purposively sampled adults will inform domain identification and item generation. An e-Delphi process involving experts in CDoH and public health will refine and confirm items followed by content validity. This will be followed by assessment of face validity for clarity and relevance. Construct validity will be assessed through exploratory and confirmatory factor analyses, using fit indices such as Minimum χ2/df, Goodness of Fit Index, Tucker-Lewis Index, Comparative Fit Index, Root Mean Square Error of Approximation and Standardised Root Mean Square Residual. Reliability will be estimated using Cronbach's alpha, and convergent and discriminant validity will be examined through correlation analyses.

ETHICS AND DISSEMINATION: Ethical approval has been obtained from the Institutional Ethics Committee, Amrita Institute of Medical Sciences, Kochi (ECASM-AIMS-2025-267). Results will be disseminated through peer-reviewed publications, conferences and policy briefs, and the validated tool will be made accessible for research and public health applications.