Question

1. True or False: Eta-squared is a more conservative measure of proportion of variance than partial eta-squared.

2. To compute partial eta-squared, it is necessary to

		partial out between-persons variability before computing proportion of variance
		partial out within-persons variability before computing proportion of variance
		partial out between-groups variability before computing proportion of variance
		partial out within-groups variability before computing proportion of variance

Answer 1

Eta squared is calculated the same way as R Squared, and has the most equivalent interpretation: out of the total variation in Y, the proportion that can be attributed to a specific X.

Eta Squared has two drawbacks, however. One is that as you add more variables to the model, the proportion explained by any one variable will automatically decrease. This makes it hard to compare the effect of a single variable in different studies.

Partial Eta Squared solves this problem, but has a less intuitive interpretation. There, the denominator is not the total variation in Y, but the unexplained variation in Y plus the variation explained just by that X. So any variation explained by other X's is removed from the denominator.

In a one-way ANOVA, Eta Squared and Partial Eta Squared will be equal, but this isn’t true in models with more than one independent variable.

The drawback for Eta Squared is that it is a biased measure of population variance explained (although it is accurate for the sample). It always overestimates it.

Answer : False

2) Answer : A

To compute partial eta-squared, it is necessary to partial out between-persons variability before computing proportion of variance.