Three different statistical procedures for identifying aptitude-treatment interactions (ATI's) are discussed with regard to statistical power. The three procedures are (1) treatment × blocks analysis of variance, (2) homogeneity of group regressions and (3) extreme groups analysis. The treatment × blocks analysis of variance offers the least power while the extreme groups analysis offers the greatest power. A general discussion of statistical power is presented along with a FORTRAN function for the calculation of power. A FORTRAN program is also provided for the calculation of extreme groups analyses. As a special feature, this program allows the researcher to determine what form of extreme groups analysis will provide maximum power.
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