The Efficacy and Effectiveness of Online CBT - Jeroen Ruwaard

3.4. Discussion 57on anxiety were lower (d = .5 vs. d = 1.0). Furthermore, the differences in efficacymay be obscured by differences in control group improvements. Andersson andco-workers (2005) found a small effect of d = .2 in the control group, whereas thepresent study revealed a large effect in the control group (d = .8). Clearly, it wouldbe interesting to compare both approaches directly.3.4.2 LimitationsWe did not make use of a structured diagnostic interview to establish a formal diagnosisof depression or dysthymia. Face-to-face interviewing was not an option, given thatwe aim to develop fully internet-based treatment. Instead, we used cut-off scores ofself-report scales to determine the clinical status of the participants. Although theconsequences of these cut-offs are known, observer-rated diagnoses may add to thevalidity of the results. Telephonic diagnostic interviews may provide a future solution.A second limitation concerns the generalizability of the results. We excludedrespondents with BDI-IA scores indicating severe depression (> 29). Therefore, theresults of the present study should not be generalised to individuals with severedepression. The generalizability of results might be further limited by our exclusioncriteria. Note, however, that most excluded respondents were rejected becausethey suffered from posttraumatic stress or panic disorder, for which effective onlinealternative treatments exist, or because of dissociation and suicidal ideation, for whichwe presently consider online treatment unsuited given the lack of face-to-face contact.Another limitation is that the period between pre-test and posttest differed somewhatbetween the groups studied in this trial. To control for this discrepancy, weused linear extrapolation to estimate the changes in the control group. As a result,the observed improvements in the control group were more pronounced. Thus, theextrapolation resulted in a conservative estimate of treatment efficacy. Nevertheless,replication studies should aim to avoid such corrections, for example by using theobserved estimate of treatment duration (16 weeks), or by measuring both groupsafter a fixed interval, regardless of treatment progress. As a final limitation, weremind the reader that the long-term follow-up study was uncontrolled, and that itincluded only those participants who completed treatment. The positive outcome ofthe long-term follow-up needs to be corroborated, preferably by a comparative study.