A randomized controlled trial is the study design that can provide the most compelling evidence that the study treatment causes the expected effect on human health. The advantages of proper randomization include:
It eliminates bias in treatment assignment, specifically selection bias and confounding.
It facilitates blinding (masking) of the identity of treatments from investigators, participants, and assessors.
It permits the use of probability theory to express the likelihood that any difference in outcome between treatment groups merely indicates chance.
The reference by Poolman et al reviewed all JBJS articles from 2003-2004 and found that 31% of the studies used modified outcome questionnaires, and frequently did not describe how they modified the questionnaires. They also recommend that operating surgeons do not collect the outcome data, in order to minimize bias.
Einhorn TA, O’Keefe RJ, Buckwalter JA (eds): Orthopaedic Basic Science: Foundations of Clinical Practice, ed 3. Rosemont, IL, American Academy of Orthopaedic Surgeons, 2007, pp 87-101
Poolman RW, Struijs PA, Krips R, et al: Reporting of outcomes in orthopaedic randomized trials: Does blinding of outcome assessors matter? J Bone Joint Surg Am 2007;89:550- 558
PMID:17332104 (Link to Abstract)