Abstract

The aim of this paper is to offer a practical guideline for researchers investigating parapsychological phenomena or phenomena to choose appropriate sample sizes to achieve a statistical power equal or above 0.80. The availability of different meta-analyses related to different parapsychological phenomena, offer a sufficient estimation of the expected effect size, usually in the range of small to very small. With these measures, we estimated the numerosity of sample sizes necessary to achieve a level of statistical power that can facilitate the replication of the observations of different parapsychological phenomena. We discuss ways to deal with the investigation of phenomena with very small effect sizes requiring very large sample sizes.