Objective To describe the level of obligation conveyed by deontic terms (words such as “should”, “may”, “must” and “is indicated”) commonly found in clinical practice guidelines.

Design Cross-sectional electronic survey.

Setting A clinical scenario was developed by the researchers, and recommendations containing 12 deontic terms and phrases were presented to the participants.

Participants All 1332 registrants of the 2008 annual conference of the US Agency for Healthcare Research and Quality.

Main outcome measures Participants indicated the level of obligation they believed guideline authors intended by using a slider mechanism ranging from “No obligation” (leftmost position recorded as 0) to “Full obligation” (rightmost position recorded as 100.)

Results 445/1332 registrants (36%) submitted the on-line survey; 254/445 (57%) reported that they have experience in developing clinical practice guidelines; 133/445 (30%) indicated that they provide healthcare. “Must” conveyed the highest level of obligation (median=100) and least amount of variability (interquartile range=5.) “May” (median=37) and “may consider” (median=33) conveyed the lowest levels of obligation. All other terms conveyed intermediate levels of obligation characterised by wide and overlapping interquartile ranges.

Conclusions Members of the health services community believe guideline authors intend variable levels of obligation when using different deontic terms within practice recommendations. Ranking of a subset of terms by intended level of obligation is possible. Matching deontic terminology to the intended recommendation strength can help standardise the use of deontic terminology by guideline developers.