Determining sample size for a test of the equality of alpha coefficients when the number of part-tests is small

In some measurement studies, the researcher seeks to compare the internal consistency reliability coefficients (alpha(1) and alpha(2)) of 2 rating scales or 2 observational techniques. In planning such studies, the investigator must determine the sample size (e.g., the number of participants or raters) that should be used if the power of the rest of the null hypothesis is to be adequate. In this article, tables are derived that enable the researcher to determine what sample sizes are required to attain a specified power against a given alternative to the hypothesis of equality of 2 values of Cronbach's alpha coefficient. The tables cover situations in which either independent or dependent samples of participants or raters are used to estimate the reliability coefficients.