Gene Glass Combines Everyone's Small Studies Into One Answer

Meta-analysis statistically combines the results of multiple independent studies that tested the same question, pooling their effect sizes, weighted by sample size and methodological quality, into a single estimate that is more precise and more resistant to any one study's flaws than any individual study on its own. The educational psychologist Gene V. Glass coined the term in 1976, developing the method to settle a contested question in psychotherapy research where dozens of small individual studies had produced inconsistent results that no single study could resolve, and showing that combining them statistically could reveal a consistent overall effect the individual studies had each been too small to detect clearly.

Claims about religious practice, that meditation measurably reduces stress, that prayer affects health outcomes, that a given ritual produces a documented psychological benefit, are typically tested across many small independent studies rather than one large one, and those studies frequently disagree. Meta-analytic methodology is how the atlas distinguishes a claim genuinely supported by the pooled weight of the evidence from one resting on a single favorable study that later, larger or better designed studies failed to replicate.