Séance-room and other large-scale psychokinetic phenomena have fascinated humankind for decades. Experimental research has reduced these phenomena to attempts to influence (a) the fall of dice and, later, (b) the output of random number generators (RNGs). The meta-analysis combined 380 studies that assessed whether RNG output correlated with human intention and found a significant but very small overall effect size. The study effect sizes were strongly and inversely related to sample size and were extremely heterogeneous. A Monte Carlo simulation revealed that the small effect size, the relation between sample size and effect size, and the extreme effect size heterogeneity found could in principle be a result of publication bias.

Institute for Border Areas of Psychology and Mental Hygiene H. Bo ¨sch, F. Steinkamp, and E. Boller's (2006) meta-analysis, which demonstrated (a) a small but highly significant overall effect, (b) a small-study effect, and (c) extreme heterogeneity, has provoked widely differing responses. After considering D. B. Wilson and W. R. Shadish's ( 2006) and D. Radin, R. Nelson, Y. Dobyns, and J. Houtkooper's (2006) concerns about the possible effects of psychological moderator variables, the potential for missing data, and the difficulties inherent in any meta-analytic data, the authors reaffirm their view that publication bias is the most parsimonious model to account for all 3 findings. However, until compulsory registration of trials occurs, it cannot be proven that the effect is in fact attributable to publication bias, and it remains up to the individual reader to decide how the results are best and most parsimoniously interpreted.