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