Randomised Controlled Trials are quantitative experimental studies in which individuals are allocated to receive one of multiple clinical interventions or a control at random. Interventions that individuals may be subjected to in Randomised Controlled Trials include treatment (or placebo), prevention strategies, screening programs, diagnostic tests, different settings, or educational models.
RCTs are excellent at providing answers to questions seeking the effectiveness of different interventions.
Hierarchy of evidence
Characteristics of Randomised Controlled Trials
- include one (or more) treatment arm and a control arm
- participants are allocated at random to one of the groups
- both the participants and the researchers remain unaware of which intervention was allocated to the groups
- each group is treated identically (except the intervention being investigated)
- participants are analysed within their assigned group, irrespective of the allocated intervention
- analysis aims to estimate the size of the difference in predefined outcomes between the groups
What Makes RCTs Superior To Other Research Methods?
In RCTs, which are experimental studies, exposure is controlled by the researcher. On the other hand, in cohort and case control studies, which are observational studies, the researcher follows the outcomes related to exposures over which they had no control.
Whilst other study designs can point out associations between an intervention and an outcome, they are not able to exclude the effect of an extraneous factor linked to both.
Randomised Controlled Trials ~ Parallel Design vs Crossover Design
There are 2 types of RCTs:
- Parallel Design: in this type of RCT, each group of participants is exposed to one of the interventions only; intervention assigned to each group is determined at random
- Crossover Design: in this type of RCT, each participant is subjected to all the interventions within the study in successive periods; first intervention allocated is determined at random
Blinding – Single vs Double
In the ideal RCT, both the participants and the clinicians are left unaware of which participants are receiving which intervention. This is what we refer to as blinding. Blinding reduces the risk of ascertainment bias (when some members of the target population are more likely to be included in the sample than others) and observation bias (when a researcher’s expectations, opinions, or prejudices influence what they perceive or record in a study). An RCT without any type of blinding is referred to as an open trial.
Ethical Considerations
Prior to the start of a Randomised Controlled Trial, there needs to be genuine doubt on whether one intervention is superior to another, as well as a balance between any potential risks to the participants and potential benefits to future patients.
Thus, one needs to keep in mind that it is unethical to expose participants to a presumably inferior or potentially harmful intervention. It is also unethical to deprive patients from an intervention which is presumed to be beneficial.
RCTs Limitations
- recruitment difficulties
- blinding difficulties
- costly and time consuming
- requires large sample size to detect small intervention effects
- not ideal for screening or interventions with rare outcomes or outcomes emerging after long intervals
- randomisation may not be possible due to patient preferences or clinicians’ decisions
Critically Appraising Randomised Controlled Trials
- critical appraisal of randomised controlled trials depend on reporting accuracy
- results tend to emphasise statistical significance instead of clinical importance
- small sample size leads to insufficient ability in detecting significant differences
- poor randomisation reporting
- poor blinding
- no follow up
CASP TOOL for RCT
CASP Tool for critically appraising Randomised Controlled Trials can be found here.
To view blogpost featuring Cochrane videos on all types of studies please click here.
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Claire is keen about public education on health-related subjects as well as holistic patient-centered care. She is also passionate about spreading awareness on the negative effects that domestic abuse leaves on its victims’ mental, emotional, social and physical wellbeing.
Claire aspires to continue studying following completion of her Nursing Degree, because she truly believes in lifelong education.
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