title: 'Heads I win, tails you lose': testing directional alternative hypotheses in ecological and evolutionary research.
abstract: Whenever experiments make a priori predictions about the direction of change in some parameter, one-tailed test statistics offer a potentially large gain in power over the corresponding two-tailed test. This gain is rarely used in ecology and evolution because of (1) the belief that one-tailed procedures are unavailable for most statistical tests and (2) an inherent dilemma in one-tailed tests: how do we handle large parameter changes in the unanticipated direction? The first problem is a misconception, whereas the second is easily resolved by recognizing that one- and two-tailed tests are simply extremes in a continuum of testing options.
authors.affiliation: Dept. of Biology, University of California, Santa Cruz, CA 95064, USA.
authors.forename: W R
authors.initials: WR
authors.lastname: Rice
authors.forename: S D
authors.initials: SD
authors.lastname: Gaines