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Round your numbers in rank tests: exact and asymptotic inference and ties

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Abstract

Non-parametric statistical tests are commonly used in the behavioral sciences. Researchers need to be aware that non-parameteric methods involving ranks can perform unreliably as a result of very small amounts of noise added in the storage and manipulation of values by computers, causing spurious reduction in the number of ties. In order to avoid this problem, researchers should round values to an appropriate number of decimal places prior to the ranking procedure to ensure that data points whose values cannot be separated according to the precision of their measurement are recorded as having identical rank. We also recommend exact rather than asymptotic evaluation of p values in non-parametric statistical tests.

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Authors and Affiliations

  1. Department of Mathematics and Technique, RheinAhrCampus, Koblenz University of Applied Sciences, Südallee 2, 53424, Remagen, Germany

    Markus Neuhäuser

  2. Division of Ecology and Evolutionary Biology, Faculty of Biomedical and Life Sciences, Graham Kerr Building, University of Glasgow, Glasgow, G12 8QQ, Scotland, UK

    Graeme D. Ruxton

Authors
  1. Markus Neuhäuser
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  2. Graeme D. Ruxton
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Correspondence to Markus Neuhäuser.

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Communicated by LZ Garamszegi

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Neuhäuser, M., Ruxton, G.D. Round your numbers in rank tests: exact and asymptotic inference and ties. Behav Ecol Sociobiol 64, 297–303 (2009). https://doi.org/10.1007/s00265-009-0843-1

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  • DOI: https://doi.org/10.1007/s00265-009-0843-1

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