The worst performance rule with elderly in abnormal cognitive decline

•The WPR might improve the understanding of cognitive functioning in MCI or dementia patients.•A consistent WPR pattern emerged in a memory clinic sample using SRT as WPR task and across five estimates of psychometric g.•These findings expand the WPR paradigm to elderly suffering abnormal cognitive decline.

Compared to best performances, worst performances on multi-trial psychometric tests often show stronger correlations with other g-loaded cognitive tests, which is known as the Worst Performance Rule (WPR). While worst performances may be more sensitive or specific to cognitive decline, clinical psychometric research and neuropsychological practice tends to neglect the WPR. Here, we examined the WPR-paradigm relative to abnormal cognitive decline. Specifically, we studied the WPR with binned simple reaction time task responses when rank-correlated with five different estimates of psychometric g within a memory clinic sample (n = 103) of elderly diagnosed with either Mild Cognitive Impairment (MCI) (n = 53) or dementia (n = 50). Three of the g-estimates were composite scores constructed from 2, 6, and 28 established test scores. Results showed a consistent WPR-pattern in the whole sample for each of the five estimates (block design rs = − 0.201 to − 0.120; digit span rs = − 0.284 to − 0.112; g2 rs = − 0.311 to − 0.162; g6 rs = − 0.314 to − 0.107; g28 rs = − 0.269 to − 0.121). Our findings contradict classical test theory, and highlight the underused potential of the WPR when assessing cognitive dysfunction in elderly patients.