Design and content validation of an instrument measuring user perception of the persuasive design principles in a breastfeeding mHealth app: A modified Delphi study

Background: Persuasive design principles are increasingly employed in mHealth apps for motivating users and promoting healthy behaviours among individuals. However, how the persuasive design principles are perceived by the mHealth app users remains unclear. Aim: To develop and validate the content validity of an instrument designed to measure the user's perceptions of the persuasive design principles assimilated in a breastfeeding mHealth app. Methods: A critical review of the literature guided the development of the research instrument. The developed instrument was refined and validated through a two-round modified Delphi process. Ten experts drawn from academic and clinical settings evaluated the items through two content validity indicators, relevance, and clarity and provided narrative feedback. The content validity of the instrument was determined by calculating the Content Validity Index (CVI). Content validity indicators at the scale-level (S-CVI) and item-level (I-CVI) were calculated. Results: The results demonstrated high content validity index of individual items in the instrument. All items in the instrument reached an excellent I-CVI ≥ 0.78 for both relevance and clarity except one item. The overall content validity index of the instrument using the average approach was moderate to high (S-CVI/Ave was 0.89 and 0.92 for relevance and clarity, respectively). The developed research instrument is composed of 5 constructs representing 24 items: (1) primary task support, (2) dialogue support, (3) system credibility support, (4) social support and (5) perceived persuasiveness. Conclusions: Using a modified Delphi approach, the development and validation of the research instrument demonstrated moderate to high content validity for measuring users’ perceptions of the persuasive design principles assimilated in a breastfeeding mHealth app. The evidence from this study supports that the research instrument is valid, relevant, and clear.