This article describes and field-tests the improvement rate difference (IRD), a new effect size for summarizing single-case research data. Termed “risk difference” in medical research, IRD expresses the difference in successful performance between baseline and intervention phases. IRD can be calculated from visual analysis of nonoverlapping data, and is easily explained to most educators. IRD entails few data assumptions and has confidence intervals. The article applies IRD to 166 published data series, correlates results with three other effect sizes: R2, Kruskal-Wallis W, and percent of nonoverlapping data (PND), and reports interrater reliability of the IRD hand scoring. The major finding is that IRD is a promising effect size for single-case research.

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Five experiments tested the idea that instructing a witness to close their eyes during retrieval might increase retrieval success. In Experiment 1 participants watched a video, before a cued-recall test for which they were either instructed to close their eyes, or received no-instructions. Eye-closure led to an increase in correct cued-recall, with no increase in incorrect responses. Experiments 2-5 sought to test the generality of this effect over variations in study material (video or live interaction), test format (cued- or free-recall) and information modality (visual or auditory details recalled). Overall, eye-closure increased recall of both visual detail and auditory details, with no accompanying increase in recall of false details. Collectively, these data convincingly demonstrate the benefits of eye-closure as an aid to retrieval, and offer insight into why hypnosis, which usually involves eye-closure, may facilitate eyewitness recall.

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