Effect Size

• Effect sizes provides a measure of the clinical importance of an empirical finding

• There are many types of effect size

Cohen’s D

• Cohen’s d is a measure of effect size that scales mean differences in standard deviation units

• Classifications for Cohen’s d– Small effect = 0.2 standard deviation– Medium effect = 0.5 standard deviation– Large effect = 0.8 standard deviation

r

• r measures the proportion of variance that the IV accounts for in the dv

• Classification for r– Small effect = less than .25– Medium effect = .25 to .40– Large effect = .40 or more

η (Eta)

• η (eta) is a measure of effect size for ANOVA– It measures the proportion of total variance that is

accounted for by group differences

• Classifications for η– Small effect = less than .25– Medium effect = .25 to .40– Large effect = .40 or more

Effect Size for Goodness of Fit

• r is used to measure effects for a goodness of fit test

• Classifications for r– Small effect = less than .30– Medium effect = .30 to .50– Large effect = more than .50

Effect Size for Test of Independence

• φ (phi) is used to measure effect size for a test of independence

• Classifications of φ– Small effect = less than .30– Medium effect = .30 to .50– Large effect = more than .50