Physical inactivity has been recognized as one of the leading risk factors that account for cardiovascular disease, type-2 diabetes, stroke, hypertension, etc., with the World Health Organization labeling it as the fourth leading risk factor for global mortality. Research has shown that persuasive technology (PT) can be leveraged as a motivational/supportive tool in tackling the physical-inactivity problem. In particular, research shows that persuasive health applications (PHAs) are more likely to be effective if they are theorydriven and tailored to the target audience. Yet, most existing PHAs on the market are neither theory-driven nor tailored to the target audience. Rather, their designers often employ a one-size- fits-all approach. This makes it difficult to know what design decisions are effective or ineffective among a given target audience. To bridge this gap, I proposed a framework, called the "EMVE-DeCK Framework," grounded in Bandura's Triad of Reciprocal Determinism, for designing, implementing and evaluating tailored PT interventions. Basically, the EMVE-DeCK Framework employs "Theory" and "Technology" to explain and change "Behavior."

Moreover, research shows that culture can be leveraged as a personalization mechanism for tailoring PHAs to the target users to make them more effective. However, there is limited cross-cultural research|grounded in theory and empirical evidence|on the effectiveness of culture-based tailoring, especially comparative studies involving understudied populations in the PT research landscape. Hence, using the Hofstede's cultural framework (individualism vs. collectivism), Social Cognitive Theory, Technology Acceptance Model and the EMVE-DeCK Framework, I conducted a number of comparative studies to understand the culture-speci c determinants of physical-activity behavior and the acceptance of a proposed PHA. I used the ndings to inform the design, implementation and evaluation of two versions of a tness app called BEN'FIT - personal version (PV) and social version (SV) - aimed to motivate bodyweight exercise at home.

In this dissertation, using the EMVE-DeCK Framework and Canada/United States (individualist culture) and Nigeria (collectivist culture) as a case study, I describe:​ (1) the cross-cultural user studies and empirical f indings that informed the PT intervention;​ (2) the design and implementation of the culture-tailored PHA;​ (3) the evaluation of the overall and culture-tailoring e ectiveness of the PHA in a eld setting. Finally, based on empirical evidence, I present a set of validated PT design guidelines in the eld for designing and tailoring PHAs to users in the individualist and collectivist cultures.

This dissertation makes three major contributions to PT research in the Human-Computer-Interaction domain. Firstly, it demonstrates how theory and culture can be employed in the design and development of PT interventions to motivate behavior change. Secondly, it reveals and validates in the eld how the individualist and collectivist cultures fundamentally differ in their motivational mechanism of behavior change. Thirdly, it provides an in-the- field validates PT design guidelines for developing tailored PHAs for the two main types of culture. In the physical-activity domain, the dissertation is the rst to conduct a theory-driven, in-the-fi eld cross-cultural PT research that focuses on an understudied population from Africa (Nigeria) and compare its ndings with those of a widely studied population from North America (Canada/United States).