Abstract Background Internet-based cognitive behavioral therapy (iCBT) for the treatment of depression has proven to be an effective and accessible option. However, iCBTs tend to have low adherence rates, which may negatively impact their effectiveness. One such iCBT program is the browser-based, proven-effective iFightDepression (iFD) tool. An app-based version of the iFD tool is the iFD app, which was developed to improve usability with a smartphone. The iFD app provides enhanced usability and a more optimized user experience on mobile devices. Additionally, it offers more comfortable interaction with worksheets, reduced text with added videos, and quicker access to the program via the smartphone icon. These improved usability on smartphones and could have an impact on adherence. Objective This study investigated (1) whether adherence parameters, that is, the number of worksheets , the number of sessions , and the number of workshops , significantly differed between users of the iFD app and the iFD tool and (2) exploratorily whether symptom reduction (delta Patient Health Questionnaire-9 PHQ-9 scores) differed after 5 to 9 weeks between the iFD app and the iFD tool, after controlling for covariates. Methods We used t tests to compare data from 56 participants using the iFD app for 8 weeks with data from 172 participants using the iFD tool in a previous 6-week study. Exploratively, symptom reduction was compared between formats. A multiple regression model was calculated with the delta PHQ-9 score as the dependent variable and format, baseline PHQ-9 score, adherence, current psychotherapy, antidepressants, age, and sex as independent variables. Results There was no significant difference between the iFD tool and the iFD app in terms of the number of sessions per week ( t 67.393 =0.920; P =.36; corrected P =.36), the number of workshops ( t 76.368 =–1.217; P =.30; corrected P =.36), and the number of worksheets per week ( t 74 =0.984; P =.33; corrected P =.36). We found no difference in delta PHQ-9 scores between the iFD app and the iFD tool, and baseline PHQ-9 scores were the only significant predictor ( b =–0.61; P <.001). Conclusions Despite the improved availability of the app version in daily life, there were no significant differences in the use parameters we analyzed and no differences in symptom reduction. This study provides the first evidence that adherence to iCBT content is comparable for browser- and app-based interventions and that symptom reduction is similar for both formats. However, this study used a convenience sample, and therefore, the results must be interpreted with caution. Notably, in the study of the iFD tool, guidance was provided by the study assistants in a standardized manner. In the pilot study on the iFD app, the amount of guidance varied substantially, as it was provided by the participants’ health care practitioners. These differences in guidance could also have an influence on adherence.
Scholze et al. (2026) studied this question.