GROUP-SIZE AND MEASURES OF GROUP-LEVEL PROPERTIES - AN EXAMINATION OFETA-SQUARED AND ICC VALUES

The eta-squared (eta(2)) from a one-way random effects ANOVA is an ind ex commonly used to estimate group-level properties of data in multile vel research. Under some circumstances; however, eta(2) values provide biased estimates of the group-level properties. Biased estimates occu r because the magnitude of the eta(2) in a one-way random Effects ANOV A is partially a function of group size. In this paper, the relationsh ip between group- size and eta(2) is described, and a simulation verif ying the relationship between group size and eta(2) is conducted. The simulation demonstrates the conditions under which eta(2) does and doe s not provide a biased estimate of group-level proper ties. The paper concludes by (a) discussing corrections for eta(2), and (b) providing guideline. for calculating estimates of group-level properties in samp les having unequal group sizes.