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related pages: [My Educ. refs] [effect size] [Hawthorne effect] [placebo effect] [regression to mean] [Shayer's road map]

RCTs: summary of the gold standards, and degrees of merit, for expt. designs

By Steve Draper,   Department of Psychology,   University of Glasgow.

(In this web page, any literature references given or implied should be (although may in fact not be) on my page of educ. lit refs.)

This page overlaps with another /~steve/educ/meth.html and I'm not sure whether to merge them.

add the stuff (now in my hawth/placebo page) on sham interventions as an important control against Ps' expectations

The idea is: that in medicine at least, the gold standard for a study is the RCT (randomised controlled trial). I've found it can be a good way to discuss and report on less-than-gold trials, by providing a checklist of what inferences from the data are and are not supported in a given trial. Furthermore, there are some other terms to note for similar use in common designs e.g. "two-arm trial". And some extra grades on top of RCT (platinum standard?) Merit score of quality from 1 upwards: 1. Trial (intervention not correlational) 2. Randomised (not convenience sample, not self-selected. Stratified?) Allocation concealment: preventing the people receiving participants from knowing what condition the new P will be placed in until after that allocation has been done. 3. Controlled by: baseline ==? within-participants design Cross-over trials. 2-arm trials. by placebo by "treatment as usual" i.e. treatment before the new idea being tested was proposed. by baseline: a larger group getting no treatment 4. Blinded: (e.g. by placebo) then blinding 0, 1, 2, 3 [triple-blind] 5. Merely formal blinding vs. actually testing that the participant didn't know whether the condition was placebo or "treatment" — despite formal blinding, many patients can tell from side-effects. 6. Co-morbidities excluded 7. Co-drugs excluded (confounded by potential multi-drug interactions?)


What is so great about randomisation and comparative trials is that they can balance out, cancel out, factors which you do not understand nor even suspect exist ("unknown unknowns"). In a way, this is absolutely important in science because to exist, science must have been able to create knowledge about some factor without knowing in advance all the factors that exist.

RCTs in themselves address key biasses, but not all. Other sources remain, though they too may have commonly used solutions e.g. blinding.
(Jadad, A. R. and Enkin, M. W. (2007) "Bias in Randomized Controlled Trials" in Randomized Controlled Trials: Questions, Answers, and Musings Second Edition, Blackwell Publishing Ltd, Oxford, UK. doi: 10.1002/9780470691922.ch3 book chapter)

Common problems with both medical and educational trials

Common problems with medical trials

Common problems with education trials

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