Abstract: We report the results of a meta-analysis on forced-choice ESP studies
which used targets such as card symbols, numbers, letters, and so forth. For the
period 1987 to 2010, a homogeneous dataset of 72 forced-choice studies yielded
a weak but significant mean effect size (ES) of 0.01 (Stouffer Z = 4.86, p = 5.90 °—
10–7). There was no evidence that these results were due to low-quality design or
selective reporting. The clairvoyance studies did not produce a significantly higher
mean ES than the precognition studies, and target type did not make a difference to
effect size. We note that effects do not vary between investigators, but we did find
suggestive evidence that the number of choices per trial is inversely related to the p
value. We also found evidence of a linear incline in ES values indicating that effect
sizes have increased over the period 1987 to 2010. Suggestions are made that might
help facilitate further increases in effect sizes.


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