On percentile norms in neuropsychology: proposed reporting standards and methods for quantifying the uncertainty over the percentile ranks of test scores

John R. Crawford, Paul H. Garthwaite, Daniel J. Slick

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Normative data for neuropsychological tests are often presented in the form of percentiles. One problem when using percentile norms stems from uncertainty over the definitional formula for a percentile. (There are three co-existing definitions and these can produce substantially different results.) A second uncertainty stems from the use of a normative sample to estimate the standing of a raw score in the normative population. This uncertainty is unavoidable but its extent can be captured using methods developed in the present paper. A set of reporting standards for the presentation of percentile norms in neuropsychology is proposed. An accompanying computer program (available to download) implements these standards and generates tables of point and interval estimates of percentile ranks for new or existing normative data.

Original languageEnglish
Pages (from-to)1173-1195
Number of pages23
JournalClinical Neuropsychologist
Issue number7
Publication statusPublished - 2009


  • neuropsychological assessment
  • interval estimates
  • confidence intervals
  • credible intervals
  • test norms
  • non-normal data
  • percentile ranks
  • Bayesian methods
  • reporting standards
  • statistical reform
  • computer scoring
  • interval estimation
  • confidence-limits
  • proportion
  • samples

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