External Validity and Model Validity: A Conceptual Approach for Systematic Review Methodology

Table 1

EVAT* for assessing the external validity of both RCTs and non-randomized studies in health care interventions.

	Well Covered (++)	Adequately Addressed (+)	Poorly Addressed (−)
(1) Recruitment; Did the study identify the source population for participants and describe how the participants were recruited from that source population?
(2) Participation**; Were those subjects who participated in the study representative of the entire source population from which they were recruited?
(3) Model validity; Were the staff, places, and facilities where the patients were treated representative of the treatment that the majority of patients would typically receive?

∗EVAT is a modified tool based on the GAP checklist and the Downs and black checklist for measuring study quality.
**This question is only applicable if question number 1 was answered, either well covered or adequately addressed. If marked poorly addressed, this question would also have to be marked poorly addressed because the reviewer would not have an understanding of the source population as described in the report.