Bidirectional experimental effects

Bidirectional experimental effects cannot be demonstrated by comparing measures of central tendency. Three approaches to the problem were considered: a test of homogeneity of variance, a comparison of control and experimental quartile frequencies by means of the chi-square test of association, and the cumulative-percentage-difference (CPD) curve--a graphic tool for demonstrating bidirectional effects. Two tests of significance were developed based on the CPD curve's maximum and minimum values. All 3 tests were first put to use analyzing simulated data, which incorporated 6 different patterns of experimental effect. The results of 100 repetitions of the simulations are summarized. Next, the results of a lexical-decision experiment with partial-word preview were analyzed using the procedures considered. The report ends with a presentation of guidelines for the use of the bidirectional tests.