Table 1

Comparison of Several Methods of Evaluating a Medical Intervention
Method	Strengths		Weaknesses

Randomized controlled trial	1.	No temporal bias	1.	Cost and effort
	2.	No selection bias	2.	Recruitment

Observational cohort study	1.	No temporal bias	1.	Cost of data collection
			2.	Selection bias if an
				important risk factor is
				omitted or not
				adequately quantified

Paired availability design	1.	Lessens selection bias	1.	Assumptions in Table 2

Baker et al. BMC Medical Research Methodology 2001 1:9 doi:10.1186/1471-2288-1-9