East Carolina University
Department of Psychology

One-Tailed NHST

    In Psychology, the norm is to employ non-directional rather than directional tests of hypotheses.  Some have teased us about this, noting that theory in Psychology is so retarded that it cannot even predict the direction of associations between variables.  Directional hypotheses are met with suspicion, as some will expect that the prediction was made a posteriori, after observing the data.  This suspicion is likely to be greatest with the p value is less than .05 for the directional test and over .05 for the nondirectional test.

    IMHO, there are cases where a strong argument could be made for the use of directional tests, three of which are detailed below.

birds flying

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This page most recently revised on the 29th of January, 2013.