Meta-analysis of free-response studies, 1992-2008: assessing the noise reduction model in parapsychology

Psychol Bull. 2010 Jul;136(4):471-85. doi: 10.1037/a0019457.

Abstract

We report the results of meta-analyses on 3 types of free-response study: (a) ganzfeld (a technique that enhances a communication anomaly referred to as "psi"); (b) nonganzfeld noise reduction using alleged psi-enhancing techniques such as dream psi, meditation, relaxation, or hypnosis; and (c) standard free response (nonganzfeld, no noise reduction). For the period 1997-2008, a homogeneous data set of 29 ganzfeld studies yielded a mean effect size of 0.142 (Stouffer Z = 5.48, p = 2.13 x 10(-8)). A homogeneous nonganzfeld noise reduction data set of 16 studies yielded a mean effect size of 0.110 (Stouffer Z = 3.35, p = 2.08 x 10(-4)), and a homogeneous data set of 14 standard free-response studies produced a weak negative mean effect size of -0.029 (Stouffer Z = -2.29, p = .989). The mean effect size value of the ganzfeld database was significantly higher than the mean effect size of the standard free-response database but was not higher than the effect size of the nonganzfeld noise reduction database [corrected].We also found that selected participants (believers in the paranormal, meditators, etc.) had a performance advantage over unselected participants, but only if they were in the ganzfeld condition.

Publication types

  • Meta-Analysis

MeSH terms

  • Acoustic Stimulation* / methods
  • Dreams / psychology
  • Humans
  • Hypnosis / methods
  • Meditation / methods
  • Meditation / psychology
  • Meta-Analysis as Topic
  • Models, Psychological*
  • Parapsychology / methods*
  • Photic Stimulation / methods
  • Relaxation / psychology
  • Reproducibility of Results
  • Research Design
  • Telepathy