Table 2.

Requirements for Paired Availablity Design

Requirement	Specific Criteria
Stable population	1.	Hospital serves one geographic area or
		is military medical center
	2.	No in- or out- migration
	3.	Eligibility criteria constant over time
	4.	No underlying change in prognosis
		over time
Stable treatment	1.	Other patient management constant
		over time
Stable evaluation	1.	Evaluation criteria constant over time
Stable preference	1.	No publicized credible reports
	2.	No direct-to-consumer advertising
Effect of the intervention on outcome does	1.	Effect of intervention does not depend
not change with a change in availability		on when the intervention was given
(only applicable when some in "before"		during the course of disease
group receive intervention)	2.	No learning curve for the intervention