8.64 Sample size, effect size, and ESP: Bem (2011) reports nine experiments in which he presents evidence for extrasensory perception (ESP). For example, in Experiment 1, participants were shown two “curtains” side by side on a computer screen and told that there was a picture behind one curtain and nothing behind the second curtain. Participants were better than chance at guessing which curtain was hiding the picture, but only for erotic pictures. Following is a table of the sample size and effect size (Cohen’s

d) for each of the 9 studies in Bem’s 2011 report.

Experiment Sample Size Cohen’s d 1 100 0.25 2 150 0.20 3 100 0.25 4 100 0.25 5 100 0.22 6 150 0.15 7 200 0.09 8 100 0.19 9 50 0.42

a. What do you notice about the relation between sample size and effect size?

b. What problem or problems are suggested given the relation between sample size and effect size?