Wr. Rice et Sd. Gaines, HEADS I WIN, TAILS YOU LOSE - TESTING DIRECTIONAL ALTERNATIVE HYPOTHESES IN ECOLOGICAL AND EVOLUTIONARY RESEARCH, Trends in ecology & evolution, 9(6), 1994, pp. 235-237
Whenever experiments make a priori predictions about the direction of
change in some parameter, one-tailed test statistics offer a potential
ly large gain in power over the corresponding two-tailed test. This ga
in is rarely used in ecology and evolution because of (1) the belief t
hat one-tailed procedures are unavailable for most statistical tests a
nd (2) an inherent dilemma in one-tailed tests: how do we handle large
parameter changes in the unanticipated direction? The first problem i
s a misconception, whereas the second is easily resolved by recognizin
g that one and two-tailed tests are simply extremes in a continuum of
testing options.