The intervention Don’t Panic Online (DPO) has been described above. The participants in the intervention group were coached by Master’s-level Clinical Psychology students who had received brief training and were supervised by one of the investigators. It should be noted that in the Netherlands, Master’s-level Clinical Psychology students have very little practical experience. Every week, the participants received an email from their coach, asking how they were doing and whether they were experiencing any difficulty in following the programme. The coaches responded to questions about the course and the associated exercises. They were instructed to reply only briefly to questions about the participant’s mental health. Participants were supported for a maximum of 3 months. The total weekly time spent on each participant differed considerably per participant and per week, but on average, it took between 5 and 10 min.

Participants in the randomised controlled trial were recruited from the general population, mostly from websites. Inclusion criteria were being aged 18 and above, mild to moderate panic symptoms (a score of 5–15 on the Panic Disorder Severity Scale-Self Report; PDSS-SR) and no or low suicide risk. No restrictions were imposed on diagnosis or the use of pharmacotherapy or psychotherapy. Of 368 applicants, 126 met these criteria and were randomly allocated to the intervention (n = 63) or to the control group (n = 63). Participants in the control group received access to DPO after completing the post-treatment measurement (3 months after baseline), although they did not receive guidance. While waiting, they had access to a website that contained information about the symptoms of panic and agoraphobia. This website included advice to contact a general practitioner, in case the participant had further questions about panic symptoms and its treatment. All of the participants in the control group and the intervention group were free to seek any (additional) help they might require. In the intervention group, 34 of 63 participants (54 %) completed the post-treatment questionnaires. Slightly more participants in the control group completed the post-treatment questionnaires (39 of 63 or 62 %).

As mentioned above, the intention-to-treat analyses did not yield a significant effect, while the completers-only analyses did. Completers were not actually full completers, but had completed the first four modules (or more) of the course (n = 17). Sixteen of these 17 participants also filled in post-treatment questionnaires. A track-and-trace system kept a record of the dates on which participants completed a module. Figure 3.1 shows the adherence of the intervention (guided) group and the waiting-control (unguided) group. Four participants in the intervention group (6 %) completed all six modules within 3 months. There were 30 participants in the intervention group who did respond to the post-treatment measurement but did not complete all six modules. These participants were asked why they had not finished. The most frequently reported reasons involved time constraints (n = 13), life events (n = 5) and symptoms so severe that the individual was unable to follow the programme (or parts thereof) or carry out the homework assignments (n = 5).

The treatment adherence was lower in the study on DPO than in previous studies of guided Internet interventions for PD/A (Table 3.1). There are a number of possible explanations (see Van Ballegooijen et al. 2013), where the type of guidance could be a main factor that explains the low adherence. When viewing Fig. 3.1, there is only a small difference between the adherence of participants in the guided intervention group and the participants in the unguided group that started once they completed their 3-month wait. This indicates that the guidance had little impact on the adherence. The adherence rate of both groups more closely resembles the figures of unguided Internet interventions for PD/A (Farvolden et al. 2005; Klein et al. 2011) than the adherence rates of previous studies of guided ICBT for PD/A. A completion rate of 1 % or 10 % is reported in the studies on unguided ICBT (Farvolden et al. 2005; Klein et al. 2011). As described above, the guidance to DPO was supposed to be minimal and focussed on retaining participants’ motivation. Questions about the participant’s mental health were only briefly addressed. Possibly, such minimal coaching is not sufficient to support participants in ICBT for PD/A and interaction with a therapist is needed. This is further discussed in the Discussion section of this chapter.