When I wrote a book about Evidence Based Medicine back in 2006
- I talked about empirical evidence to support the use of certain research methodologies like blinding and allocation concealment. Since that time, many more studies have appeared
- more than you or I could easily keep track of. Thankfully
- the folks at the Agency for Healthcare Research and Quality commissioned a report to look at studies that empirically evaluate the bias reduction of several popular approaches used in randomized trials. These include
selection bias through randomization (sequence generation and allocation concealment); confounding through design or analysis; performance bias through fidelity to the protocol
- avoidance of unintended interventions
- patient or caregiver blinding and clinician or provider blinding; detection bias through outcome assessor and data analyst blinding and appropriate statistical methods; detection/performance bias through double blinding; attrition bias through intention-to-treat analysis or other approaches to accounting for dropouts; and reporting bias through complete reporting of all prespecified outcomes.
The general finding was that failure to use these bias reduction approaches tended to exaggerate treatment effects
- but the magnitude and precision of these exaggerated effects was inconsistent.
Nancy D Berkman
- P Lina Santaguida
- Meera Viswanathan
- and Sally C Morton. The Empirical Evidence of Bias in Trials Measuring Treatment Differences. Available at http://www.ncbi.nlm.nih.gov/books/NBK253181/.