Rationale While widespread use of high-quality CDRs can benefit practitioners, patients, and health-care systems, the development process for these tools is extremely resource-intensive, and rigorous development in no way guarantees widespread use. A tool to examine acceptability of early-stage CDRs would be useful.

Methods A 12-item scale was developed, pilot-tested, and then included into 4 larger surveys of practicing emergency physicians from four countries (AUS, CAN, UK, US; total n = 1290), in the context of two CDRs: the Canadian C-Spine Rule (CS) and the Canadian CT-Head Rule (CT). Respondents answered questions on a 6-point Likert scale; scale scores ranged from 0-5. In addition to typical item and internal consistency analyses, construct validity was measured in part by testing 4 hypotheses: 1) Scale scores for both rules should vary predictably by country, the highest scores coming from Canada; 2) CDR users should give higher scores than non-users; 3) Among users, OADRS scores should be higher for consistent users; 4) Among non-users, scores should be higher for those who would consider using the rules in the future.

Results Internal consistency was high, ranging from 0.79 to 0.83 for CS, and from 0.81 to 0.87 for CT. Multi-factor ANOVAs with scale scores as the outcome showed 1) Canada scored highest on overall scale scores (Mean scores:AUS 3.36, CAN 3.91, UK 3.52, US 3.38; main effect p < .001; posthoc test p < .001); 2) Scores were higher among users than non-users (CS means: 3.83 vs. 2.96, p<.001; CT means 3.77 vs. 3.01, p<.001); 3) Scores were higher among consistent users (CS means: Always 4.30; Most of the time 3.93, Some of the time 3.23; CT means: Always 4.34; Most of the time 3.92, Some of the time 3.36; p < .001 in both cases); and 4) Among non-users, scores were higher for those who would consider use (CS means: Yes 3.40; No 2.57; CT means: Yes 3.45; No 2.64, p < .001 for both. Interactions were generally small or non-significant.

Conclusions The OADRS might serve as an ‘early-warning system' for CDR producers wanting to know whether a CDR will be considered acceptable by the target audience.