Carlos S. Alvarado, PhD, Research Fellow, Parapsychology Foundation

Lance Storm and Patrizio E. Tressoldi have just published a meta-analysis of experimental ESP studies that have examined the sheep-goat effect. The article’s title is “Gathering in More Sheep and Goats: A Meta-Analysis of Forced-Choice Sheep-Goat ESP Studies, 1994–2015” (Journal of the Society for Psychical Research, 2017, 81, 79-107).

Lance Storm 2

Lance Storm

Patrizio Tressoldi 5

Patrizio Tressoldi

Here is the abstract:

The terms ‘sheep’ and ‘goat’ were introduced by Gertrude Schmeidler — sheep are those who accept the possibility of ESP occurring under given experimental conditions, while goats are those participants who reject the possibility. In statistical tests of psychic ability, Schmeidler found that sheep tended to score above chance, while goats (rather than scoring at chance) tended to score below chance. This scoring differential is known as the sheep-goat effect (SGE). This study is a meta-analysis of the SGE in forced-choice literature, being a continuation from where Lawrence (1993) left off. The period of analysis was 1994 to 2015. The authors retrieved 49 studies reported by 43 investigators. The mean ES for ESP = .045, mean z = 0.75, Stouffer Z = 5.23 (p = 8.47 × 10-8), and the mean trial-based SGE = 0.034, mean z = 0.24, Stouffer Z = 1.67 (p = .047). Thus, our SGE is on par with Lawrence’s reported “r = 0.029”. There was no relationship between study quality and ESP effect or SGE, but there was a significant incline in the SGE over a period of 22 years. The SGE did not vary significantly with belief measure used. Bayesian analysis of the same dataset yielded results supporting the ‘frequentist’ finding that the null hypothesis should be rejected. These and other findings are generally comparable to Lawrence’s, altogether indicating a “belief-moderated communications anomaly” in the forced-choice ESP domain that has been effectively uninterrupted and consistent for almost 70 years.