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as to the person’s own past responses. The underlying rule base was complex, resulting in around 20,000 possible unique reports. The system proved to be considerably more effective than providing non-tailored materials or simply allowing people to answer the questions and draw their own conclusions. Use of the system resulted in a self-reported 22-26% smoking-cessation point-prevalence (people who said they had not smoked in the last 24 hours; an intermediary outcome associated with long-term cessation) [20]. This means the system was nearly as effective at helping people quit smoking as intensive clinic-based interventions. 2.2. Choice of therapy for breast cancer The BresDex decision aid provided a variety of different forms of information to help women with breast cancer in deciding between breast-conserving surgery with radiotherapy or mastectomy [21]. The Theory of Planned Behaviour has also been shown to predict behaviour in decisions such as choice of cancer therapy. As with other decision aids, the goal of this system was to help the patient come to a decision that is in line with her values. The authors used an extended version of the theory which included the construct “anticipated regret.” The decision aid consisted of video clips of enacted patient experiences (all constructs), patient photos (attitudes and anticipated regret), videos of health professionals (attitudes, subjective norms, and perceived behavioural control), information on further treatment (attitudes and anticipated regret), a Your Surgery Options section (attitudes and anticipated regret), an It’s Your Choice section (subjective norms and perceived behavioural control), a What’s Next section (behavioural control), and a “decision support” tool which visually summarized the patient’s responses to other items as a tally of pros and cons for each option (subjective norms and perceived behavioural control). The decision aid also offered information on the causes, types, and consequences of breast cancer, in line with the Common Sense Model of Illness Representations (a model of coping behaviour in disease). The effect of the decision aid was studied in a sample of 54 women using questionnaires administered before and after using the system. “Readiness to make a decision” improved significantly after using the system, as measured by the DelibeRATE score (increase from a mean score of 65 to 76, p < 0.001). However, knowledge of breast cancer did not change, as measured by a 10-point breast cancer knowledge scale (mean score = 8.3 before and 8.5 after; p = 0.202). Most women preferred breast-conserving surgery both before and after using the system, although slightly more preferred it after (27/54 participants before and 30/54 participants after). 2.3. Exercise Active Living Every Day is an internet-delivered program designed to encourage exercise and reduce cardiovascular disease risk factors in sedentary adults [22]. Participants are screened for their level of readiness to change based on the Transtheoretical model. They are then matched to a (fictional) virtual participant at the same level of readiness to change. They can read about their virtual partner's progress, and receive reading material tailored to their state of change. The material includes activities such as Setting Goals (consciousness-raising), Scouting Physical Activity in Your Community (environmental re-evaluation, helping relationships), and Mall Walking (counter-conditioning, reinforcement management). Participants also keep a S.MedlockandJ.C.Wyatt /HealthBehaviourTheory inHealth Informatics 153