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What is the chance that this study is clinically significant? A proposal for Q values
1VA Outcomes Group, Department of Veterans Affairs Medical Center, White River Junction, Vt., USA. gregory.froelich@hitchcock.org
Context:
Clinicians who use the medical literature to guide their practice need to make judgments about the clinical significance of medical interventions.
General Question:
How likely is an intervention to be clinically worthwhile?
Specific Research Challenge:
Given the results of a study, determining the probability that the true effect of an intervention is at least as great as some minimum worthwhile effect.
Current Approach:
P values are widely used to convey the probability of observed effects arising by chance if there truly is no effect. By convention, P values less than 0.05 are interpreted as being "statistically significant."
Potential Difficulties:
Statistical significance is often confused with clinical significance.
Alternate Approach:
A different probability could be reported, a probability I call a Q value. A Q value is the probability that the true effect of an intervention is at least as great as some minimum worthwhile effect. Q values are calculated in a manner analogous to that used for P values, except that the null hypothesis becomes a minimum worthwhile effect instead of no effect. Q values encourage researchers and clinicians to be explicit about what they think a worthwhile effect is and could help shift the focus of study interpretation away from arbitrary statistical conventions.