Development and validation of novel scales to determine pharmacist's care for herbal and dietary supplement users

BACKGROUND: The factors associated with the provision of pharmacist's care (PCare) for herbal and dietary supplement (HDS) users are multidimensional. These factors should be investigated to assess the needs for community pharmacists (CPs) to provide the service. However, at present, there are no validated and reliable theory-based instruments to measure the factors.

OBJECTIVES: The study aims to develop and validate scales (direct and indirect) based on a modified Theory of Planned Behavior (TPB) to measure factors associated with the provision of PCare for HDS users by Thai CPs.

METHOD: Item generation for the scales was based on the theoretical constructs of the modified TPB framework, literature review, and authors' previous qualitative study. Draft items were then subjected to content validity and face validity. Psychometric testing was carried out among CPs in Bangkok, Thailand. Refinement of the scales utilized factor analysis and validity was assessed using factor analysis and Rasch analysis. Internal consistency reliability and construct reliability were used to assess the scales' reliability.

RESULTS: Initially, the direct and indirect scales contained 15 and 28 items, respectively and were reduced to 12 and 16 items, after experts' review. Factor analysis further reduced the number of items of the indirect scale to 13. For both scales, confirmatory factor analysis showed model-data fit. Each construct of the direct scale was significant predictors of intention. Moreover, each construct of the direct scale correlated positively and significantly with the respective construct of the indirect scale, signifying concurrent validity. No misfit item was identified in the Rasch analysis and the majority of items were invariant across gender. Internal consistency reliability and construct reliability of the scales were acceptable.

CONCLUSION: This study presents the development and validation of theoretically-grounded scales to measure the factors associated with the provision of PCare for HDS users by Thai CPs.