Question

Review the scenario and answer the questions below:

1. One of the studies included in a meta-analysis reported statistically significant relationship (r = 0.63, P < .001) between the research variables. What is the effect size?

2. Another study reported that the postintervention mean on a scale was 26.6 (standard deviation [SD] = 8) for the treatment group and 18.5 for the control group (SD = 8). What is this effect size?

Answer 1

1) Pearson's correlation coefficient , r is used as effect size when we want to access relationship between variables

Here r =0.63

Thus effect size is 0.63

This is a large effect size

Note : Measure of effect size

upto 0.3 :small

upto 0.5 medium

>0.5 : large

2) Here we have to find effect size based on difference between means

We calculate Cohen's d effect size

where

=8

Thus

Effect size is 1.01 , which is large effect size

Note : Cohen's d

small effect :0.2

medium effect : 0.5

large effect : 0.8 or more