The Use of the Johnson-Neyman Confidence Bands and Multiple Regression Models To Investigate Interaction Effects: Important Tools for Educational Researchers and Program Evaluators.

N

32

Computer Software; Evaluation Methods; Interaction; Outcomes of Education; Predictor Variables; Regression (Statistics); Research Methodology

When investigating the impact of predictor variables on an outcome variable or measuring the effectiveness of an educational program, educational researchers and program evaluators cannot ignore the possible influences of interaction effects. The purpose of this paper is to present a procedure that educational researchers can follow in order to increase their understanding of the nature of the interaction effect between a treatment variable and a continuous independent variable. This technique involves the use of three separate analytical techniques implemented in three steps. First, the interaction effect is statistically tested using a multiple regression model. Second, the interaction effect is plotted, and if the interaction effect is disordinal, the intersection point of the regression lines is calculated. Third, the Johnson-Neyman confidence limits are calculated. A list of the computer commands that can be used in conjunction with the Statistical Package for the Social Sciences (SPSS) PC+ computer software to calculate the Johnson-Neyman confidence limits is provided. In addition, this three-step analytical procedure is applied to a set of efficacy data that was collected in a study of the FOCUS instruction model developed by G. Russell (1992) to illustrate how it can be used by researchers and program evaluators. An appendix presents the computer program for the calculation of the confidence limits. (Contains 2 figures, 2 tables, and 16 references.) (Author/SLD)

1998

ED411256