INTRODUCTION: The study examined the perceived value of different forms of evidence (i.e., randomized controlled trials and retrospective cohort analyses study designs) among physicians and pharmacists (N=780). Research participants read three abstracts (for each of three fictitious drugs) that varied type of claim (cost, cost-effectiveness, and effectiveness) and study design. They rated the perceived value of the study in determining formulary recommendations on seven items. METHODS: Factor analysis was used to derive weights for a single measure of value that ranged from 0.735 (low value) to 5.145 (high value). RESULTS: Four-way ANOVAs indicated that cost-effectiveness (mean=3.19) and effectiveness (mean=3.11) data were of more value than cost data (mean=2.84, p<.0001). Also, formulary-affiliated physicians (mean=3.10) found the studies to be of more value than hospital pharmacy directors (mean=2.93, p<.02). A significant two-way interaction indicated that pharmacy directors valued retrospective cohort analyses more than randomized trials regardless of type of claim. In contrast, physicians valued randomized trials more than retrospective cohort analyses (p<.001). Manipulation checks indicated some difficulty identifying the purpose of individual studies. While most respondents could correctly identify cost-effectiveness and effectiveness studies (between 77% and 92% correctly identified these studies), there was confusion regarding cost studies. Almost half of the participants (between 42% and 57%) characterized these studies (which were described as "cost-minimization" analyses) as cost-effectiveness studies. Pharmacy directors (49%) were more likely to mischaracterize the cost-minimization studies compared to the physician groups (approximately 40% of these groups) (chi square=20.29, p<.02). CONCLUSIONS: The results suggest that the multidisciplinary make-up of formulary committees is important to assure the incorporation of multiple forms of evidence in decision making. Also, more attention to the study design is essential to evaluate the value of various forms of evidence for formulary decisions.