Eta squared is a measure of effect size that is commonly used in ANOVA models. It measures the proportion of variance associated with each main effect and interaction effect in an ANOVA model. The value for Eta squared ranges from 0 to 1, where values closer to 1 indicate a higher proportion of variance that can be explained by a given variable in the model. The following rules of thumb are used to interpret values for Eta squared:
A p-value can only tell us whether or not there is some significant association between two variables, but a measure of effect size like Eta squared can tell us the strength of association between the variables.
Eta Squared(η2): η2= SSeffect/SStotal. SS effect is the sum of squares of an effect for one variable and SS total is the total sum of squares in the ANOVA model.