Behind the software: The impact of Unobtrusiveness, Goal Setting and persuasive features on BMI.

Background: Studies have demonstrated that interventions targeting weight loss and body mass index (BMI) reduction can be successful, although the specific factors that influence their effectiveness are still unclear. Behavior change support systems (BCSS) are an approach that aims to help users in their efforts to modify their behavior. A useful tool for assessing BCSS is the Persuasive Systems Design model (PSD), where different features and postulates can be employed. However, it is unknown whether the grouping of software features and design principles, along with behavioral traits, provide a better combination to achieve effective BMI reduction.

Objective: This study investigates the impact of PSD features, postulates behind the design, and behavioral traits on BMI reduction after six months of utilizing a mobile health behavior change support system (mHBCSS).

Methods: We examined a subset of 96 individuals from a randomized controlled trial using a mHBCSS for a period of six months. Data was analyzed using Partial Least Squares Structural Equation Modeling (PLS-SEM).

Results: We found that 15.3 % in the variance of BMI reduction was explained by the ability of setting goals. Furthermore, users who perceive a system as highly persuasive are more likely to establish goals (R = 0.207). Among PSD features, Dialogue Support and Primary Task Support explained 54.9 % of the variance in Perceived Persuasiveness. In addition, both Dialogue Support and Credibility Support have a mutual effect on Primary Task Support (R = 0.685). Finally, the system's unobtrusiveness explained 41.1 % of the variance in Dialogue Support.

Conclusion: PSD framework and behavior change theories provide significant influence on BMI reduction. Setting a clear and organized objective assists individuals in successfully pursuing their intended results. The findings of this study can help developers and health professionals decide which PSD features and postulates to include to make mHBCSS interventions targeting BMI reduction more effective.