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To test if Fogg’s theory improved sign-up rates for the NHS organ donation website, an online study was conducted in which 889 participants were randomized to use one of two versions of the website over a 3 week period, one with characteristics previously identified as signalling credibility (University logo, privacy statement, references, etc.) and one with characteristics of low credibility (advertisements, broken links, non-secure site for entering form data). This study showed no difference in the number of participants registering as an organ donor (176/466 or 37.8% in the "credible" variant, 160/423, again 37.8% in the "low credibility" variant). However, the kind of decision being made in this study – whether to allow your organs to be harvested for transplant after death – was very different from the kind of decision targeted by Fogg’s persuasive technology theory – whether to purchase an item on an eCommerce website. Thus, perhaps not surprisingly, the theory was simply not valid in this context. Another example of an intervention which did not go as planned was the Personally Controlled Health Management System for Asthma [25]. This was a web-based self- management system for asthma, with the primary goal of helping patients develop a written Asthma Action Plan. The system contained three "patient journeys," which were designed around the Health Belief Model. The first journey aimed to increase perceived susceptibility and emphasizes the importance of having a written plan in the event of an asthma attack, the second addressed perceived barriers by providing the information needed to formulate a plan, and the third addressed self-efficacy by providing encouraging tips in monthly emails. They also provided a "cue to action" by allowing patients to book a consultation online. The system was also informed by the Transtheoretical model, in that the three journeys can be viewed as appropriate for different stages of change and the social cognitive theory by incorporating social features such as polls and forums. However, only 20% of eligible participants ever logged in more Figure . Effect of use of theory in internet-based behaviour change interventions. Based on data from Webb et al. [3] 4 S.MedlockandJ.C.Wyatt /HealthBehaviourTheory inHealth Informatics 155