Table 1.

Specialized classifications of randomized controlled trials

Type	Description	Strengths	Limitations
Cluster	Randomization of subjects as a group rather than on individual basis	Can study interventions that cannot be directed toward selected individuals Can control for contamination across individuals (i.e., when one individual’s behavior can influence another’s)	Needs more subjects to reach statistical power than standard RCT
Explanatory	Individual randomization of very selective subjects in a highly controlled setting	Useful to test efficacy (i.e., whether an intervention causes a specific biologic response) Patients blinded Excellent internal validity Good for acute disease processes	External validity and applicability to clinical practice is limited due to subject selection
Pragmatic	Individual randomization of non-selective group of patients in a regular clinical setting	Useful to test effectiveness of an intervention in everyday practice Good for chronic disease processes and complex interventions Excellent external validity and directly applicable to clinical practice	Patients unblinded Internal validity limited due to broad inclusion criteria
Expertise-based	Individual randomization of subjects to an expertise in the intervention in question	Useful when intervention is non-pharmacologic (i.e., surgical procedures)	External validity limited to only those patients receiving care from a physician with expertise skills