Why this one and not something cleverer
This is the simplest treatment on the shelf and it holds up unusually well when it is tested, which is why it is the one a course can honestly hand over.
What the research says
Ekers D, Webster L, Van Straten A, Cuijpers P, Richards D, Gilbody S (2014). Behavioural activation for depression: an update of meta-analysis of effectiveness and sub group analysis. PLoS ONE, 9(6), e100100 doi
A pooled analysis of trials of behavioural activation, which is the approach this lesson borrows from. It is the evidence base for choosing activity scheduling as the one thing to teach here rather than something more elaborate.
Richards DA, Ekers D, McMillan D, Taylor RS, Byford S, and others (2016). Cost and outcome of behavioural activation versus cognitive behavioural therapy for depression (COBRA): a randomised, controlled, non-inferiority trial. The Lancet, 388(10047), 871 to 880 doi
Behavioural activation delivered by less highly trained staff was not inferior to full cognitive behavioural therapy, and cost less. The honest limit is that not inferior is not the same as better, and the margin for calling something non-inferior is a judgement the trialists made in advance.