Using a Likelihood Heuristic to Summarize Conflicting Literature on Predictors of Clinical Outcome Following Sport-Related Concussion.

Objective: To introduce a new methodology for summarizing the results from systematic reviews-a likelihood heuristic-to the field of sport-related concussion.

Data Sources: We applied the likelihood heuristic to the results of a systematic review published by Iverson et al (2017), containing 101 studies, on the predictors of worse clinical outcome following sport-related concussion.

Study Selection: We re-examined 5 individual prognostic factors that are of clinical interest and for which there is conflicting literature (female sex = 44 studies, prior concussion history = 41 studies, loss of consciousness = 31 studies, post-traumatic amnesia = 25 studies, and retrograde amnesia = 10 studies).

Data Extraction: For each prognostic factor, likelihood ratios were generated using the (1) number of significant and nonsignificant studies, (2) study power, (3) alpha level, and (4) prior probability that the alternative hypothesis was true.

Data Synthesis: Assuming each study had 80% power and an alpha level of 5%, observing the reported number of conflicting studies for female sex, prior concussion history, and retrograde amnesia is substantially more likely if each prognostic factor is associated with worse clinical outcome following sport-related concussion. For loss of consciousness, the observed number of conflicting studies is more likely if loss of consciousness is not associated with worse clinical outcome following sport-related concussion. A secondary analysis incorporating potentially more realistic study parameters of statistical power (45%) and alpha level (25%) generates weaker likelihood evidence that the observed numbers of studies for each prognostic factor are associated with worse clinical outcome following sport-related concussion than they are not.

Conclusions: Using a likelihood heuristic with 80% power and 5% alpha level, there is very strong likelihood evidence that female sex, prior concussion history, and retrograde amnesia are associated with worse clinical outcome following sport-related concussion. The strength of likelihood evidence that prognostic factors are associated with worse clinical outcome reduces when statistical power is lower and alpha level is inflated.