Answers to the ES Questions

ANSWERS TO ES

Answers to the ES Questions

d = M1 - M2 / �[(s1�+ s2�) / 2]
   = D = 7.50 - 2.725 / �[(2.038�+ 2.592�) / 2]
   = 2.05

 

 Cohen's d

Compute Cohen's d using the two standard deviations.

How large is the d using Cohen's interpretation
of effect sizes?
d = 2t/�(df)
   = 2(9.16)�73.89
   = 2.13		 Cohen's d

Compute Cohen's d using the value of the t-test statistic.

Are the two values of d similar?
g = 2t / �N
   = 2(9.16) / �80
   = 2.05		 Hedges's g

Compute Hedges's g using the t-test statistic.

 
D = M1 - M2 / s
control 
  = 7.50 - 2.725 / 2.038
= 2.34
Glass's delta

Calculate Glass's delta using the standard deviation of the control group.
rYl = �[t� / (t� + df)]
      = �[9.16� / (9.16� + 73.89)]
     = .73		 Effect size correlation

The effect size correlation was computed by SPSS as the correlation between the iv (TREATGRP) and the dv (SUDS4), rY>l = .

Calculate the effect size correlation using the t value.
rYl = d / �(d� + 4)
     = 2.05 / �(2.05� + 4)
     = .72		 Effect size correlation

Use Cohen's d to calculate the effect size correlation.