Understanding adherence to web-based interventions

Although eHealth technologies and especially web-based interventions for the promotion of health and health related behavior have been shown to be effective, the impact is hindered by non-adherence: while many eHealth interventions reach a large group of participants, not all of these participants complete the intervention and may therefore not benefit as much from the intervention as they could. In this thesis, non-adherence is investigated by means of empirical studies into two web-based interventions: the Healthy Weight Assistant, an intervention aimed at healthy dietary and physical activity behavior; and Living to the Full, an intervention for the prevention of depression. Additionally, a systematic review was conducted to investigate the influence of intervention characteristics and persuasive design on adherence to web-based interventions. The comparison of adherers and non-adherers in the empirical studies has shown that adherers and non-adherers are different groups, but there are no universal predictors for adherence; rather it is important to create a match between participants and the intervention to improve adherence. Second, the human centered development process of Living to the Full and the investigation of the reasons for use of the Healthy Weight Assistant showed that participants expect a web-based intervention to support them in achieving their goals and to have the advantages that the Internet has to offer. Not fulfilling these expectations may well be a reason for non-adherence. Third, the systematic review showed that a persuasive design of web-based interventions, especially more use of dialogue support, increases the adherence to the intervention. The investigation of the impact of different persuasive design elements in Living to the Full showed that these persuasive design elements not always result in better adherence. Lastly, the empirical studies showed that participants do not use all features of a web-based intervention, but adherers use more features and seem to be more involved with the intervention than non-adherers. With these insights, the opportunity arises to not only hope for adherence, but to plan for adherence.