Caveat emptor: rank transform methods and interaction

• Published in: Trends in ecology & evolution (Amsterdam) Vol. 9; no. 7; pp. 261 - 263
• Main Authors: Seaman, John W., Walls, Susan C., Wise, Sharon E., Jaeger, Robert G.
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 01.07.1994; Elsevier
• Subjects: Animal, plant and microbial ecology; Biological and medical sciences; Fundamental and applied biological sciences. Psychology; General aspects. Techniques; Methods and techniques (sampling, tagging, trapping, modelling...); Statistical method; Rank statistic; Ecology; Rank transformation; Interspecific relation
• ISSN: 0169-5347; 1872-8383
• DOI: 10.1016/0169-5347(94)90292-5

When distributional assumptions for analysis of variance are suspect, and nonparametric methods are unavailable, ecologists frequently employ rank transformation (RT) methods. The technique replaces observations by their ranks, which are then analysed using standard parametric tests. RT methods are widely recommended in statistics texts and in manuals for packages like SAS and IMSL. They are robust and powerful for the analysis of additive factorial designs. Recently, however, RT methods have been found to be grossly inappropriate for use with non-additive models. This severe limitation remains largely unreported outside of the theoretical statistics literature. Our goal is to explain this shortcoming of RT methods.