Homeopathy can offer empirical insights on treatment effects in a null field

A "null field" is a scientific field where there is nothing to discover and where observed associations are thus expected to simply reflect the magnitude of bias. We aimed to characterize a null field using a known example, homeopathy (a pseudoscientific medical approach based on using highly diluted substances), as a prototype.

We identified 50 randomized placebo-controlled trials of homeopathy interventions from highly cited meta-analyses. The primary outcome variable was the observed effect size in the studies. Variables related to study quality or impact were also extracted.

The mean effect size for homeopathy was 0.36 standard deviations (Hedges' g; 95% confidence interval: 0.21, 0.51) better than placebo, which corresponds to an odds ratio of 1.94 (95% CI: 1.69, 2.23) in favor of homeopathy. 80% of studies had positive effect sizes (favoring homeopathy). Effect size was significantly correlated with citation counts from journals in the directory of open-access journals and CiteWatch. We identified common statistical errors in 25 studies.

A null field like homeopathy can exhibit large effect sizes, high rates of favorable results, and high citation impact in the published scientific literature. Null fields may represent a useful negative control for the scientific process.