“Double blind” refers to the requirement for idea pharmacological randomised controlled trials that not only the participants but also any prescribers or other staff in contact with the participants be kept blind as to what medication, typically placebo or active compound, the participant has received. This removes expectancy effects.
For psychological therapies it is generally impossible for trials to be even single blind let alone double blind (though the idea that both client and therapist might have not the faintest idea what is going on is perhaps …!)
Not to be confused with the idea of “double bind” out of the Palo Alto systemic group which was the idea that a child might be given a injunction, e.g. “You must never steal cookies” with a contradictory message perhaps in a different mode, for example a particularly loving hug and (often forgotten as it suggest the term should have been “treble bind”, an overarching constraint preventing the child escaping (usually the condition of being a child). No empirical evidence it has anything to do with psychosis as they thought but remains an interesting idea about some challenges of growing up or “Chris’s double bind”:
“You should never do RCTs of therapy: they’re illogical! <angry face>”
“But I so like that you want a career doing empirical research into therapies” <smiley face> and
“Ooops, but you’ll need to bring in grant income to have that career” <woeful grimace>.
Try also #
Hierarchy of evidence
Randomised Controlled Trials (RCTs)
Double Blind Controlled Trials (DBRCTs)
Hierarchy of evidence (and web of evidence)
ESTs (Empirically Supported Treatments)