Misprescription and misuse of one-tailed tests

LOMBARDI, C.; HURLBERT, S.

AUSTRAL ECOLOGY

Wiley-Blackwell

Año: 2009

1442-9985

Abstract One-tailed statistical tests are often used in ecology, animal behaviour and in most other fields in the biological and social sciences. Here we review the frequency of their use in the 1989 and 2005 volumes of two journals (Animal Behaviour and Oecologia), their advantages and disadvantages, the extensive erroneous advice on them in both older and modern statistics texts, and their utility in certain narrow areas of applied research. Of those articles with data sets susceptible to 1-tailed tests, at least 24 percent in Animal Behaviour and at least 13 percent in Oecologia used 1-tailed tests at least once. They were used 35 percent more frequently with nonparametric methods than with parametric ones and about twice as often in 1989 as in 2005. Debate in the psychological literature of the 1950s established the logical criterion that 1-tailed tests should be restricted to situations where there is interest only in results in one direction. “Interest” should be defined, however, in terms of collective or societal interest and not by the individual investigator. By this “collective interest” criterion, all uses of 1-tailed tests in the journals surveyed seem invalid. In his book Nonparametric Statistics, S. Siegel unrelentingly advocated the use of 1-tailed tests whenever the investigator predicts the direction of a result. That work has been a major proximate source of confusion on this issue, but so are most recent statistics textbooks. The utility of 1-tailed tests in research aimed at obtaining regulatory approval of new drugs and new pesticides is briefly described, to exemplify the narrow range of research situations where such tests can be appropriate. These situations are characterized by null hypotheses stating that the difference or effect size