• A prospective study where patients from a population of interest are randomly assigned to either a experimental (treatment) or a control group and then are followed up a specific time intervals to collect data on the outcomes of interest.
• Patients in the control group usually receive a placebo or comparative treatment generally considered already part of the standard of care.

• Considered the gold standard for helping to explain an effect
• When appropriate randomization has occurred, this design allows for washout of most population bias
• Reduced influence by confounders because they can be controlled for by the investigators
• Reduced variability in the outcome(s) being measured, thus increasing the precision of estimation (assumes proper control of confounders)
  
• Easier to blind patients than observational studies

• Generally more time consuming
• Tend to be more expensive

• Cohort Study
• Case-Control Study
• Cross-Over Study
• Parametric Statistical Analysis
• Nonparametric Statistical Analysis
  

1. Noordij M et al. Study designs in clinical research. Nephron Clin Pract 2009;113(3):c218-21.
2. Tinmouth A et al. Interventional trials: an overview of design alternatives. Transfusion 2007;47:565-67.

Editors:

• Anthony J. Busti, MD, PharmD, FNLA, FAHA
  

Last Reviewed:  July 2015