The use of waitlists as control conditions in anxiety disorders research

Current evidence suggests that the strength of the psychological control condition greatly impacts treatment outcomes. Psychological controls can be grouped into three general classes: no-treatment or waitlist (delayed treatment), attention placebo or the best available treatment comparison. Of these three, the use of the waitlist condition is the most common and is used in up to 73% of published psychological treatment studies. Many psychological interventions are in use today based on the efficacy demonstrated in waitlist controlled trials. In the field of anxiety disorders, cognitive behavioural therapy (CBT) is considered a first-line treatment. Meta-analyses in anxiety disorders have revealed that effect sizes for CBT compared to waitlist controls are much higher than those found using psychological placebos as comparators. Furthermore, waitlists have been associated with deleterious effects and have been described as "no-cebos" in related conditions such as major depressive disorder. Despite these findings, the use of waitlist controls continues to be a mainstay in the psychological anxiety disorders literature. The purpose of this paper is to examine the use of waitlists with a focus on the anxiety disorders. Methodological and ethical issues associated with waitlist controls will be explored, as well the use of alternative psychological placebos.