Worst performance rule, or not-best performance rule?

The worst performance rule (WPR) is a robust empirical finding reflecting that people’s worst task performance shows stronger relations to cognitive ability compared to their average or best performance. However, recent meta-analytic work has proposed this be renamed the “not-best-performance” rule because mean and worst performance seem to predict cognitive ability to similar degrees (with both predicting ability better than best performance). We re-analyzed data from a previously published latent-variable study to test for worst vs. not-best performance across a variety of reaction time tasks in relation to two cognitive ability constructs: working memory capacity (WMC) and task-unrelated thought (TUT) rate. Using two methods of assessing worst performance—ranked-binning and ex-Gaussian-modeling approaches—we found evidence for both worst and not-best performance rules. WMC followed the not-best performance rule (correlating equivalently with mean and worst RTs) but TUT propensity followed the worst performance rule (correlating more strongly with worst RTs). Additionally, we created a mini-multiverse following different outlier exclusion rules to test the robustness of our findings; our findings remained stable across the different multiverse iterations. We provisionally conclude that the worst performance rule may only arise in relation to cognitive abilities closely linked to (failures of) sustained attention.