What is clinically significant improvement in cognitive behavioral therapy for insomnia? A scoping review of randomized controlled trials

In randomized controlled trials (RCTs), the primary focus is often on between-group differences in mean outcomes. However, to evaluate the efficacy of a treatment it is equally important to consider how many patients achieve a meaningful clinical response, which requires careful operational definitions. To review RCTs on cognitive behavioral therapy for insomnia (CBT-I) to determine how clinically significant improvement including response, remission and recovery are defined. 519 publications were included in this scoping review. Excluding secondary analyses, 380 unique RCTs on CBT-I remained of which 55 had defined response, 95 remission, five recovery and 102 had used another term. 185 records had not investigated clinical significance. The most common definition of response was “reduction of ≥ 8 on Insomnia Severity Index (ISI) total score in comparison with pre-treatment” (33 records). For remission, it was “ISI total score < 8” (70 records). In contrast, no definition of recovery was used more than once. When none of these three terms were applied, there was variability in how clinical significance was defined. Almost half of the published CBT-I RCT’s did not mention clinical significance. Recommendations are provided for which definitions to use for non-response, response, remission and recovery.