Response to Bierman and Spottiswoode (2026)

Abstract

This is a reply to Bierman and Spottiswoode’s (B&S) assertion that the between-studies “decline effect” (DE) in psi research is present in all experimental protocols related to anomalous cognition (AC; a.k.a. extra-sensory perception; ESP) and psychokinesis (PK). While B&S utilized non-parametric Spearman rho correlations to identify declines across AC and PK databases, we defend the robustness of our original meta-regression approach. Furthermore, we reanalyzed our original results, and the B&S results, taking into account the moderator effect of the number of trials or participants for the presentiment data on the effect sizes. The results were not very different from our original findings, showing that only two of six AC protocols indicated statistically significant declines, while all four PK protocols exhibited statistically significant declines. However, these databases are largely obsolete, lacking data from the last 20 years, and two of them involve very limited time spans. Our conclusion is that B&S’s interpretation overstates the observed findings, thus reaffirming our original stance: “there is no evidence of a general DE across different experimental protocols in psi research”.