Abstract
Persuasive strategies have been implemented in various ways in persuasive systems to motivate behaviour change. However, there is no empirical evidence regarding whether or not the effectiveness of persuasive systems varies based on implementation choices and why. To address this gap, we conduct a large-scale study involving 568 participants to investigate the perceived persuasiveness or effectiveness of different implementations of each strategy in the same system. We focused on six (6) popular strategies from the Persuasive Systems Design (PSD) model: self-monitoring, suggestion, reward, cooperation, social role, and normative influence. Our results show that the perceived persuasiveness of distinct implementations of the same strategy varies. For instance, people perceive Social Role strategy implemented as communication between a user and a "human" therapist as significantly more persuasive than implementing the strategy as communication between a user and a "non-human" therapist. Also, implementing Suggestion strategy as a list of suggestions/tips accessible via a menu is perceived as significantly more persuasive than contextual pop-up tips. We perform thematic analysis of qualitative comments from participants to examine the reasons for their implementation choices (why). We also offer practical design guidelines for tailoring persuasive systems based on our findings.