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What is a randomized controlled trial?

Randomized controlled trials (RCT) are scientific research studies that examine the cause and effect relationship between an intervention and outcome. In RCTs, subjects are randomly assigned to either an intervention group (the group receiving a treatment) or a control group (the group not receiving a treatment). The control group exists as a standardized group of comparison. The random assignment and control group aspects of the study design reduces bias and error.  RCTs are regarded as the gold standard for experimental design. 

When should you use a randomized controlled trial?

A randomized controlled trial is often used when a researcher is attempting to find an association between an intervention or treatment and some outcome. Research participants are randomly assigned to a control group (no treatment or a placebo treatment) or the experimental group. Additionally, the research participants or the researcher are often not told which group they are inorthe researcher is not aware of which group a participant is in (single-blind study), or the research participantsand the researcher do not know what group an individual is assigned to (double-blind study). These steps help to reduce bias or consciously manipulate the data so that any treatment-outcome association observed is more likely to be accurate and reliable. 

What is an example of a randomized controlled trial?

If a researcher wanted to see if a very high dose of supplemental vitamin D3 (50,000 IUs) one time per month was as effective as a modest dose of supplemental vitamin D3 (1000 IUs) daily in improving serum vitamin D levels in individuals who were vitamin D deficient they may randomly assign a group of 120 participants to either the treatment dose of 50,000 IUs of vitamin D3 one time per month or the control group of 1000 IUs of vitamin D3 daily so that 60 participants are in each group. At baseline, 3 months, and 6 months serum vitamin D3 levels were analyzed in all individuals and statistically analyzed. At 6 months, or the end of the study, both groups were no longer vitamin D deficient, however, individuals in the treatment group had 1.2-times higher levels of serum vitamin D3 compared to the individuals in the control group. The researcher concluded that a high dose of 50000 IUs of vitamin D3 one time per month appears to be as effective in increasing serum vitamin D3 levels as a moderate daily dose of 1000 IUs. 

What are the advantages of a randomized controlled trial?

The advantages of using a randomized controlled trial (RCT) study design is to limit the amount of bias or manipulation of data. This study design also makes it easier to blind to mask participants, researchers, or both to which group or intervention is being given. Furthermore, RCT designs have clearly identifiable populations or study group characteristics and results can be analyzed with fairly well known statistical tools such as mean, median, or standard deviation. 

What are the disadvantages of a randomized controlled trial?

The disadvantages of using a randomized controlled trial (RCT) study design is often the cost of the study and the amount of time it may take to properly analyze if a treatment has an effect. Since RCT studies are often made up of volunteer research participants, if may be difficult to enroll enough participants to accurately estimate the effect of the treatment, the sample population may not be representative of the whole population, and there could be a significant number of participants who drop out of the study due to the treatment or the length of time. 

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Medically reviewed by:

Kristin Ricklefs-Johnson, Ph.D., RD

Kristin is an RDN who also earned her Ph.D. in Nutrition from Arizona State University with an emphasis on insulin resistance, lipid metabolism disorders, and obesity. She completed her post-doctoral fellowship at Mayo Clinic where she focused on nutrition-related proteomic and metabolic research. Her interests include understanding the exact mechanism of action of various genetic variations underlying individual predispositions to nutrition-related health outcomes. Her goal is to help all individuals prevent chronic diseases and achieve long, healthy lives through eating well.

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