Question

A researcher conducted a one-sample z-test, and found a significant effect with the sample mean equaling 24 (n = 20), the population mean equaling 19, and the population standard deviation equaling 5. What is the effect size using Cohen’s d? [G&W Chp. 8]

		Cohen’s d equals 0.33
		Cohen’s d equals 0.66
		Cohen’s d equals 1.00
		Cohen’s d does NOT equal any of the above values.

Answer 1

Suppose we assume that μ represents the mean of the population of interest and μ0 represents a value to which the mean is to be compared and standard deviation is σ, then the effect size is represented by d where

? = |? − ?0|/ σ

so d=|19-24|/5=1

Thus

Cohen's d equals 1.00

Correct option is (C)