waitlist control, where people get nothing

psychoeducational, where people get some kind of educational content about mental health but not therapy

existing nonpsychological service, like physical checkups with a nurse

existing therapy, so not placebo but current treatment

pharmacological placebo, where they're given a placebo pill and told its psychiatric medication for their concern

A kind of "nerfed" version of the therapy, such as supportive therapy where the clinician just provides empathy etc but nothing else

How to interpret results depends on the control.

It's relevant to debates about general vs specific effects in therapy (rapport, empathy, fit) versus specific effects (effects due to specific techniques of a specific therapy).

Bruce Wampold has written a lot about types of controls although he has a hard nonspecific/general effects take on therapy.