Discovery Lab Answers

The Checker Effect

The checker effect refers to the phenomenon where psi-task outcomes (particularly precognition scores) vary systematically depending on who scores or evaluates the data, independent of subjects’ expectations. It was first reported by Feather and Brier in 1968 and has been revisited in subsequent research.

The Core Finding

Feather and Brier’s original observation was striking: when precognition run outcomes were divided between two scorers, performance differed based on who actually checked the data—not merely on whom subjects thought would check it ^[1]. This distinction matters. If the effect were purely expectancy-driven (subjects performing better on runs they believed would be favorably evaluated), then the identity of the actual scorer should not matter. The fact that it did suggested something more than psychological expectation was at work.

Replications and Theoretical Interpretation

Weiner and Zingrone conducted conceptual replications of the Feather-Brier work across multiple series. In their earlier research, they largely confirmed the original findings and interpreted the effect as consistent with an “observer-targeting” (OT) explanation—the idea that psi-mediated effects are associated with the person doing the scoring ^[2]. However, their subsequent replication attempts produced mixed results: Series III did not confirm their previous findings, though post-hoc analysis revealed interactions between run conditions and checker effects, indicating that the effect may be more context-dependent than initially understood ^[2].

Broader Experimenter Effects

The checker effect is one manifestation of a wider class of experimenter effects in parapsychology. Houtkooper and Haraldsson found systematic differences in scoring outcomes across different experimenters in a plethysmographic ESP experiment, noting the parallel to the checker effect ^[3]. Kennedy and Taddonio distinguished between sensory experimenter effects—those mediated through psychological or social channels—and psi experimenter effects, unintentional psi that influences outcomes in relation to the experimenter’s expectations, needs, or mood ^[4]. The checker effect appears to sit in this broader landscape of how experimenters and scorers can influence psi-task outcomes, whether through conventional psychological mechanisms or through psi itself ^[5].

The effect remains heterogeneous in replication and incompletely understood, but it highlights a substantive methodological concern in psi research: the scorer’s role may not be neutral.