Editing Randomized controlled trial (section)

== Classifications ==

=== By study design ===
One way to classify RCTs is by [[study design]].  From most to least common in the healthcare literature, the major categories of RCT study designs are:<ref name="Hopewell-2010">{{Cite journal |vauthors=Hopewell S, Dutton S, Yu LM, Chan AW, Altman DG |date=March 2010 |title=The quality of reports of randomised trials in 2000 and 2006: comparative study of articles indexed in PubMed |journal=BMJ |volume=340 |pages=c723 |doi=10.1136/bmj.c723 |pmc=2844941 |pmid=20332510}}</ref>
* [[Parallel study|Parallel-group]] – each participant is randomly assigned to a group, and all the participants in the group receive (or do not receive) an intervention.<ref>{{Cite journal |vauthors=Kaiser J, Niesen W, Probst P, Bruckner T, Doerr-Harim C, Strobel O, Knebel P, Diener MK, Mihaljevic AL, Büchler MW, Hackert T |date=June 2019 |title=Abdominal drainage versus no drainage after distal pancreatectomy: study protocol for a randomized controlled trial |journal=Trials |volume=20 |issue=1 |page=332 |doi=10.1186/s13063-019-3442-0 |pmc=6555976 |pmid=31174583 |doi-access=free}}</ref><ref>{{Cite journal |vauthors=Farag SM, Mohammed MO, El-Sobky TA, ElKadery NA, ElZohiery AK |date=March 2020 |title=Botulinum Toxin A Injection in Treatment of Upper Limb Spasticity in Children with Cerebral Palsy: A Systematic Review of Randomized Controlled Trials |journal=JBJS Reviews |volume=8 |issue=3 |pages=e0119 |doi=10.2106/JBJS.RVW.19.00119 |pmc=7161716 |pmid=32224633 |doi-access=free}}</ref>
* [[Crossover study|Crossover]] – over time, each participant receives (or does not receive) an intervention in a random sequence.<ref>{{Cite book |title=Design and Analysis of Cross-Over Trials |vauthors=Jones B, Kenward MG |publisher=London: Chapman and Hall |year=2003 |edition=Second}}</ref><ref>{{Cite book |title=Linear and Nonlinear Models for the Analysis of Repeated Measurements |vauthors=Vonesh EF, Chinchilli VG |publisher=London: Chapman and Hall |year=1997 |pages=111–202 |chapter=Crossover Experiments}}</ref>
* [[Cluster randomised controlled trial|Cluster]] – pre-existing groups of participants (e.g., villages, schools) are randomly selected to receive (or not receive) an intervention.<ref>{{Cite journal |vauthors=Gall S, Adams L, Joubert N, Ludyga S, Müller I, Nqweniso S, Pühse U, du Randt R, Seelig H, Smith D, Steinmann P, Utzinger J, Walter C, Gerber M |date=8 November 2018 |title=Effect of a 20-week physical activity intervention on selective attention and academic performance in children living in disadvantaged neighborhoods: A cluster randomized control trial |journal=PLOS ONE |volume=13 |issue=11 |pages=e0206908 |bibcode=2018PLoSO..1306908G |doi=10.1371/journal.pone.0206908 |pmc=6224098 |pmid=30408073 |doi-access=free}}</ref><ref>{{Cite journal |vauthors=Gladstone MJ, Chandna J, Kandawasvika G, Ntozini R, Majo FD, Tavengwa NV, Mbuya MN, Mangwadu GT, Chigumira A, Chasokela CM, Moulton LH, Stoltzfus RJ, Humphrey JH, Prendergast AJ |date=March 2019 |title=Independent and combined effects of improved water, sanitation, and hygiene (WASH) and improved complementary feeding on early neurodevelopment among children born to HIV-negative mothers in rural Zimbabwe: Substudy of a cluster-randomized trial |journal=PLOS Medicine |volume=16 |issue=3 |pages=e1002766 |doi=10.1371/journal.pmed.1002766 |pmc=6428259 |pmid=30897095 |doi-access=free}}</ref>
* [[Factorial experiment|Factorial]] – each participant is randomly assigned to a group that receives a particular combination of interventions or non-interventions (e.g., group 1 receives vitamin X and vitamin Y, group 2 receives vitamin X and placebo Y, group 3 receives placebo X and vitamin Y, and group 4 receives placebo X and placebo Y).
An analysis of the 616 RCTs indexed in [[PubMed]] during December 2006 found that 78% were parallel-group trials, 16% were crossover, 2% were split-body, 2% were cluster, and 2% were factorial.<ref name="Hopewell-2010" />

=== By outcome of interest (efficacy vs. effectiveness) ===
{{Main|Pragmatic clinical trial}}
RCTs can be classified as "explanatory" or "pragmatic."<ref name="Zwarenstein-2008">{{Cite journal |vauthors=Zwarenstein M, Treweek S, Gagnier JJ, Altman DG, Tunis S, Haynes B, Oxman AD, Moher D |date=November 2008 |title=Improving the reporting of pragmatic trials: an extension of the CONSORT statement |journal=BMJ |volume=337 |pages=a2390 |doi=10.1136/bmj.a2390 |pmc=3266844 |pmid=19001484}}</ref> Explanatory RCTs test [[Efficacy#Medicine|efficacy]] in a research setting with highly selected participants and under highly controlled conditions.<ref name="Zwarenstein-2008" /> In contrast, pragmatic RCTs (pRCTs) test [[Effectiveness#Usage|effectiveness]] in everyday practice with relatively unselected participants and under flexible conditions; in this way, pragmatic RCTs can "inform decisions about practice."<ref name="Zwarenstein-2008" />

=== By hypothesis (superiority vs. noninferiority vs. equivalence) ===
{{main|Equivalence test}}

Another classification of RCTs categorizes them as "superiority trials", "noninferiority trials", and "equivalence trials", which differ in methodology and reporting.<ref name="Piaggio-2006">{{Cite journal |vauthors=Piaggio G, Elbourne DR, Altman DG, Pocock SJ, Evans SJ |date=March 2006 |title=Reporting of noninferiority and equivalence randomized trials: an extension of the CONSORT statement |url=https://researchonline.lshtm.ac.uk/id/eprint/12069/1/Reporting%20of%20Noninferiority%20and%20Equivalence%20Randomized%20Trials.pdf |journal=JAMA |volume=295 |issue=10 |pages=1152–1160 |doi=10.1001/jama.295.10.1152 |pmid=16522836}}</ref> Most RCTs are superiority trials, in which one intervention is hypothesized to be superior to another in a [[Statistical significance|statistically significant]] way.<ref name="Piaggio-2006" /> Some RCTs are noninferiority trials "to determine whether a new treatment is no worse than a reference treatment."<ref name="Piaggio-2006" /> Other RCTs are equivalence trials in which the hypothesis is that two interventions are indistinguishable from each other.<ref name="Piaggio-2006" />