Our goal was to describe the level of obligation imposed by deontic terms commonly found in clinical practice guidelines. We found that the interpretation of deontic terms by the health services community varies and that ranking of deontic terms by level of obligation is possible. Using an internet-based survey, we showed that “must” conveys the highest level of obligation, while “may” and “may consider” convey lower levels of obligation. “Should” and all other deontic terms we examined convey intermediate levels of obligation.
Variable interpretation of expressions used in medicine has been well documented, most notably with regard to physician interpretation of probabilities.[28
] Kong et al demonstrated that medical professionals could agree on the ranking of common probability expressions, but there was wide variation in interpretation of each expression.[31
] Similarly, our survey demonstrates a ranking of a subset of terms but considerable variability in interpretation of individual deontic expressions.
suggests members of the health services community recognise at least three levels of obligation. “Must” conveys the highest level of obligation, while “may” and “may consider” convey lower levels. Every other term we examined conveys an intermediate level. The addition of “consider” appears to decrease the level of obligation associated with “must” and “should” but does not change the impact of “may,” which already conveys the lowest level of obligation.
While the use of “consider” in a recommendation softens the obligation imposed, it also makes measuring performance and auditing adherence more difficult. Increasingly, performance measures are based on practice guidelines.[32
] Guidelines that use “consider” pose significant challenges to quality improvement teams because it is often impossible to determine whether a recommended activity was “considered.”
A guideline reader’s formula to determine level of obligation and intended adherence likely includes a plethora of linguistic and non-linguistic variables. In addition to the deontic term encountered, a reader is likely to assess such factors as the stated recommendation strength (if present,) the type of action recommended (e.g., to prescribe a medicine vs. to order an invasive procedure or test,) the severity of the patient condition under consideration, and the organisation responsible for the guideline’s development. To our knowledge, none of these other variables have been studied as potential influences on clinicians’ perception of obligation to undertake recommended actions.
Suggestions for guideline developers
If deontic terminology were used to strengthen a connection between recommendation language and expected adherence to recommendations, these data suggest that three separate levels of recommendation strength should be available to guideline developers. As long as terms conveying distinct levels of obligation were chosen (i.e., non-overlapping interquartile ranges,) guideline developers could take advantage of a natural ranking of deontic terms.
“Must” clearly defines the highest level of obligation, but we anticipate only rare usage of the term. Based on our examination of the YGRC, “must” appears in only 19 recommendations.[18
] Use of “must” or “must not” may be limited to situations where there is a clear legal standard or where quality evidence indicates the potential for imminent patient harm if a course of action is not followed. “May” is an appropriate choice for the lowest level of obligation. We suggest avoiding any expression using “consider” for reasons mentioned earlier. The impact of “not” remains a topic for future study.
“Should” is the commonest deontic verb found in the YGRC (appearing 709 times) and is an appropriate choice to convey an intermediate level of obligation. Alternatively, the intermediate level could be stratified into “should” and “is appropriate.” Overlapping ranges of obligation may be acceptable as long as guideline developers make explicit the connection between deontic terms chosen and their intended level of obligation. One strategy would be to link deontic terms to grades of recommendation strength. In this approach, the number of deontic terms used would depend on the particular grading system applied by the guideline developers.
Our response rate was low but consistent with response rates of internet-based surveys reported elsewhere.[33
] Generalisabilty to a wider population of clinicians and consumers of practice guidelines may be limited. However, our sample included key target audiences, including clinicians, developers of practice guidelines, developers of performance measures, and developers of decisions support systems.
We wrote simplified recommendation statements within a deliberately vague clinical scenario in our best effort to isolate the effect of deontic terminology from other contextual features. Use of actual, published recommendations or an examination of other deontic terms may produce different responses. We also did not take into account word preferences (e.g., the use of “shall” vs. “should”) or cultural norms (e.g., American vs. British) that may impact how people interpret and use deontic terminology. We permitted each participant to use his or her own understanding of the concept of obligation and did not measure intra-rater variability.
A focus on deontic terminology is a small but important step towards producing guidelines with more predictable influences on clinical care.[36
] “Must,” “should,” and “may” are well suited to represent three discrete levels of obligation recognized by the health services community. A standardised approach to the use of deontic terminology and the application of deontic terminology to systems for grading recommendation strength should be part of a larger set of standards for guideline development and presentation.