Power calculations in single case neuropsychology

Abstract

Researchers and clinicians in neuropsychology often compare individual patients against healthy control samples, to quantify evidence for cognitive-behavioural deficits and dissociations. Statistical methods for these comparisons have been developed that control Type I (false positive) errors effectively. However, remarkably little attention has been given to the power of these tests. In this practical primer, we describe, in minimally technical terms, the origins and limits of power for case-control comparisons. We argue that power calculations can play useful roles in single-case study design and interpretation, and we make suggestions for optimising power in practice. As well as providing figures, tables and tools for estimating the power of case-control comparisons, we hope to assist researchers in setting realistic expectations for what such tests can achieve in general.

Sample Size Justification

“…If we are interested in detecting an effect of d = 0.5 a sample size of 90 per condition would give us more than 90% power. Statistical power can be computed to determine the number of participants, or the number of items (Westfall, Kenny, & Judd, 2014) but can also be performed for single case studies (Ferron & Onghena, 1996;McIntosh & Rittmo, 2020) Although it is common to set the Type I error rate to 5%…”