HELFRICH, Wolfgang. Are There Stable Mean Values, and Relationships between Them, in Statistical Parapsychology?. Journal of Scientific Exploration, [S. l.], v. 25, n. 1, 2011. Disponível em: https://journalofscientificexploration.org/index.php/jse/article/view/15. Acesso em: 9 may. 2026.