Norman M. Abrahams

The use of extreme groups in assessing relationships

The relationship between variables in applied and experimental research is often investigated by the use of extreme (i.e., upper and lower) groups. Earlier analytical work has demonstrated that the extreme groups procedure is more powerful than the standard correlational approach for some values of the correlation and extreme group size. The present article provides methods for using the covariance information that is usually discarded in the classical extreme groups approach. Essentially, then, the new procedure combines the extreme groups approach and the correlational approach. Consequently, it includes the advantages of each and is shown to be more powerful than either approach used alone.

Relative costs and statistical power in the extreme groups approach

The relationship between variables in applied and experimental research is often investigated by the use of extreme (i.e., upper and lower) groups. Recent analytical work has provided an extreme groups procedure that is more powerful than the standard correlational approach for all values of the correlation and extreme group size. The present article provides procedures to optimize power by determining the relative number of subjects to use in each of two stages of data collection given a fixed testing budget.

The Impact of Number of Jobs and Selection Ratio on Classification Efficiency: An Extended Table of Brogden's Allocation Average

This article is an extension of Brodgens table of allocation averages, presented in EPM in 1959. The current table deals with up to 1,000 jobs and rejection rates ranging from 0 to 90%.

Computing Tables for the Tetrachoric Correlation Coefficient

In 1933, Chesire, Saffir, and Thurstone published their Computing Diagrams for the Tetrachoric Correlation Coefficient. Since then there have been few developments to aid the practitioner in a rapid and more accurate calculation of the tetrachoric correlation. The present study describes a set of tables for ease in determining tetrachoric correlations. Entries are provided for all X variable dichotomies and their individual Y variable dichotomies rounded to the nearest five one-hundredths in proportion form. The coefficients have been computed to 3-decimal accuracy. The development of the tables in this manner allows the researcher to determine the correlation within a given sample, as well as for populations in which the base rates differ.