Evidence from efficacy trials indicates that exposure rates to Internet-delivered interventions are low (De Nooijer, Oenema, Kloek, Brug, De Vries, & De Vries, 2005), and they may be even lower when these interventions are implemented in real life rather than in a research setting (Evers, Cummins, Prochaska, & Prochaska, 2005). Exposure of individuals to the intervention content, through use of the intervention, is necessary since attention is a prerequisite to establish desired behaviour change (McGuire, 1985). Therefore, it remains important to assess exposure to Internet-delivered interventions.
There are several measures to assess exposure to Internet-delivered interventions, such as frequency and duration of visits, but there is no gold standard. Each exposure measure relates to a different aspect of exposure (Danaher, Boles, Akers, Gordon, & Severson, 2006). One can visit an intervention very frequent, for example, but only for a short period of time. Duration of visits, on the other hand, does not necessarily give a clear picture of participants