3.7. Clinical decision threshold and minimally important difference

When important decisions are made about outcomes, it is also important to consider the minimal clinical importance of an effect size, as this is best decided before the evidence is collected and summarized, in order to avoid subjective and ad hoc decisions influenced by the available evidence.

GRADE uses the term Clinical Decision Threshold, i.e. the threshold that would change the decision whether or not to adopt a clinical action.

For binary outcomes this usually implies a risk reduction. The threshold is likely to differ according to the outcome, e.g. a mortality reduction of 10 % will be more important than a reduction of 10% in the number of patients developing a rash. For continuous outcomes, the minimally important difference is used, i.e. the smallest difference in outcome of interest that informed patients or proxies perceive to be important, either beneficial or harmful, and that would lead the patient or clinician to consider a change in management.

Notes

• A minimally important difference is measured at the individual level.
• The effect on a continuous outcome can be expressed as a mean difference, but also as the proportion of patients having a benefit that is above the minimally important difference.

Determining this threshold is not straightforward and often difficult. Expert opinion is often essential.

For a few outcomes validated thresholds exist based on evidence from surveys amongst patients, e.g. the Cochrane back pain group determined a threshold for back and neck pain. Doing a specific literature search on this topic is probably too labour-intensive and moreover, there are no universally accepted and agreed validated methods for doing so. Some rules of thumb are provided by the GRADE working group, such as an increase/decrease of 25%, but one should be cautious to apply these without a critical reflection on the context.