---
title: "Randomized controlled trial"
chunk: 7/7
source: "https://en.wikipedia.org/wiki/Randomized_controlled_trial"
category: "reference"
tags: "science, encyclopedia"
date_saved: "2026-05-05T04:26:23.353341+00:00"
instance: "kb-cron"
---

=== Economics ===
RCTs have become a staple of identifying causal inference among microeconomic studies, particularly in development economics. In 1994, Paul Glewwe, eventual Nobel Prize winner, Michael Kremer, and Sylvie Moulin started one of the earliest RCTs in an economic setting by conducting a long run intervention in a school in Kenya, publishing the results fifteen years later. Three years later in 1997, the largest field experiment in a developing context, the PROGRESA program in Mexico, was studied by a multitude of economic researchers. The impact of RCTs on the discipline has only grown, as economists have found this method as a first-best approach to causal inference identification. While not at the forefront, the use of RCTs has helped to bolster the credibility revolution in empirical microeconomics, as well as becoming popularized as a result of the need for more rigorous identification. 
Despite the shift towards using RCTs in research, there still remains division between economists on its use. John A. List, a proponent of field experiments, particularly RCTs, finds that this method differs significantly from lab experiments, and therefore provide more robust measures for identification. RCTs also offer the advantage of providing true observational data that can be used where the absence of data would make it difficult to build a causal model with. 
The American Economic Association maintains a registry of all active and completed RCTs within the discipline. The registry is free to use and is designed to ensure researchers may share information with regard to on-going field work, as well as failures or limitations of study settings. Since its founding in 2013, the AEA has tracked over 7,400 field experiments across 100 countries, with annual RCT registries growing year over year.

=== Transport science ===
Researchers in transport science argue that public spending on programmes such as school travel plans could not be justified unless their efficacy is demonstrated by randomized controlled trials. Graham-Rowe and colleagues  reviewed 77 evaluations of transport interventions found in the literature, categorising them into 5 "quality levels".  They concluded that most of the studies were of low quality and advocated the use of randomized controlled trials wherever possible in future transport research.
Dr. Steve Melia took issue with these conclusions, arguing that claims about the advantages of RCTs, in establishing causality and avoiding bias, have been exaggerated.  He proposed the following eight criteria for the use of RCTs in contexts where interventions must change human behaviour to be effective:
The intervention:

Has not been applied to all members of a unique group of people (e.g. the population of a whole country, all employees of a unique organisation etc.)
Is applied in a context or setting similar to that which applies to the control group
Can be isolated from other activities—and the purpose of the study is to assess this isolated effect
Has a short timescale between its implementation and maturity of its effects
And the causal mechanisms:

Are either known to the researchers, or else all possible alternatives can be tested
Do not involve significant feedback mechanisms between the intervention group and external environments
Have a stable and predictable relationship to exogenous factors
Would act in the same way if the control group and intervention group were reversed

=== Criminology ===
A 2005 review found 83 randomized experiments in criminology published in 1982–2004, compared with only 35 published in 1957–1981. The authors classified the studies they found into five categories: "policing", "prevention", "corrections", "court", and "community".  Focusing only on offending behavior programs, Hollin (2008) argued that RCTs may be difficult to implement (e.g., if an RCT required "passing sentences that would randomly assign offenders to programmes") and therefore that experiments with quasi-experimental design are still necessary.

=== Education ===
RCTs have been used in evaluating a number of educational interventions. Between 1980 and 2016, over 1,000 reports of RCTs have been published. For example, a 2009 study randomized 260 elementary school teachers' classrooms to receive or not receive a program of behavioral screening, classroom intervention, and parent training, and then measured the behavioral and academic performance of their students. Another 2009 study randomized classrooms for 678 first-grade children to receive a classroom-centered intervention, a parent-centered intervention, or no intervention, and then followed their academic outcomes through age 19.

== Criticism ==
A 2018 review of the 10 most cited randomised controlled trials noted poor distribution of background traits, difficulties with blinding, and discussed other assumptions and biases inherent in randomised controlled trials. These include the "unique time period assessment bias", the "background traits remain constant assumption", the "average treatment effects limitation", the "simple treatment at the individual level limitation", the "all preconditions are fully met assumption", the "quantitative variable limitation" and the "placebo only or conventional treatment only limitation".

== See also ==
Drug development
Hypothesis testing
Impact evaluation
Jadad scale
Pipeline planning
Patient and public involvement
Observational study
Blinded experiment
Statistical inference
Royal Commission on Animal Magnetism – 1784 French scientific bodies' investigations involving systematic controlled trials

== References ==

== Further reading ==