DBRCT = Double Blind, Randomised Controlled Trial

[This entry overlaps with many others, see links]

A randomised controlled trial is a way of testing whether one treatment is more (or less) effective than another by allocating (hence “controlled”) participants to the one treatment or the other at random (hence “randomised”) and looking at what happens comparing the two groups’ outcomes statistically. The “double blind” bit is crucial and means that the participants do not know which treatment they are receiving (hence “blind”) nor do the researchers/clinicians involved (hence “double” blind). The blinding removes expectancy and placebo/nocebo effects.

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Where it is possible to blind everyone to the allocations, where the outcomes are measurable and relatively short term outcomes are what matters and where you can recruit sufficient participants to have good statistical power for meaningful differences between the treatments this is the gold standard way to choose between treatments for large scale use. It is rightly required by regulatory bodies for any new drug treatments to be brought to “the market” (i.e. for use in humans). This has also become one of the pillars of “evidence based medicine (EBM)” and, more widely, of “evidence based practice (EBP)”.

It is essentially impossible to have DBRCTs large enough to detect differences between treatments in rare negative effects (side effects) hence that use of DBRCTs to regulate introduction of new treatments must be complemented by “post-marketing surveillance” to detect statistically significant associations of treatments with such rare effects. I see that post-marketing surveillance as a paradigm of one sort of practice-based evidence (PBE) as a necessary complement to the DBRCT side of EBP.

Two arm RCTs may compare a new drug with a placebo (i.e. a substance with no treatment efficacy packages to be indistinguishble from the new drug) or may compare a new drug with an existing drug. It is possible to carry out RCTs with more than two arms though rarer than those two main two-arm studies.

As well as double blind it is possible, and very desirable, that trials should be “treble/triple blind” where no-one, including the investigators and statisticians involve will know until a paper or report is finalised for release, which of the arms was which.

Paradigmatic RCTs are run under near laboratory conditions and generally with many tight exclusion criteria. This limits the generalisability of their findings and another approach is of “pragmatic trials” in which the interventions are much closer to routine practice and exclusion criteria are kept to a minimum.

It is essentially impossible for trials of psycho-social interventions to be double blind. Despite this, perhaps fifty years into the transfer of the RCT as “gold standard” from pharmaceutical interventions to the psychotherapies, that issue shows no sign of denting the relentless conduct of RCTs in our area. We are also seeing exploration of some highly psychoactive drugs like the psychotogenics (ayahuasca, LSD). I am intrigued that here too the RCT seems to continue to be regarded as vital though blinding of such trials is often demostrably not even single blind.