18. A random sample of n = 16 scores is obtained from a
population with a mean of μ = 45. After a treatment
is administered to the individuals in the sample, the
sample mean is found to be M = 49.2.
a. Assuming that the sample standard deviation is
s = 8, computer and the estimated Cohen's d to
measure the size of the treatment effect.
b. Assuming that the sample standard deviation is
s = 20, computer and the estimated Cohen's d to
measure the size of the treatment effect.
c. Comparing your answers from parts a and b, how
does the variability of the scores in the sample
influence the measures of effect size?