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. Below is a table of the sample size and effect size (Cohen’s d) for each of the nine studies in Bem’s 2011 report.

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?

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Experiment Sample size Cohen's d 1 100 0.25 150 0.20 100 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 2. 3.