UNASSIGNED: Researchers typically use Cohen\'s guidelines of Pearson\'s r = .10, .30, and .50, and Cohen\'s d = 0.20, 0.50, and 0.80 to interpret observed effect sizes as small, medium, or large, respectively. However, these guidelines were not based on quantitative estimates and are only recommended if field-specific estimates are unknown. This study investigated the distribution of effect sizes in both individual differences research and group differences research in gerontology to provide estimates of effect sizes in the field.
UNASSIGNED: Effect sizes (Pearson\'s r, Cohen\'s d, and Hedges\' g) were extracted from meta-analyses published in 10 top-ranked gerontology journals. The 25th, 50th, and 75th percentile ranks were calculated for Pearson\'s r (individual differences) and Cohen\'s d or Hedges\' g (group differences) values as indicators of small, medium, and large effects. A priori power analyses were conducted for sample size calculations given the observed effect size estimates.
UNASSIGNED: Effect sizes of Pearson\'s r = .12, .20, and .32 for individual differences research and Hedges\' g = 0.16, 0.38, and 0.76 for group differences research were interpreted as small, medium, and large effects in gerontology.
UNASSIGNED: Cohen\'s guidelines appear to overestimate effect sizes in gerontology. Researchers are encouraged to use Pearson\'s r = .10, .20, and .30, and Cohen\'s d or Hedges\' g = 0.15, 0.40, and 0.75 to interpret small, medium, and large effects in gerontology, and recruit larger samples.

Neurodevelopmental disorders such as autism affect one-eighth of all U.S. newborns. Yet scientists, accessing the same data and using Bradford-Hill guidelines, draw different conclusions about the causes of these disorders. They disagree about the pesticide-harm hypothesis, that typical United States prenatal pesticide exposure can cause neurodevelopmental damage. This article aims to discover whether apparent scientific disagreement about this hypothesis might be partly attributable to questionable interpretations of the Bradford-Hill causal guidelines. Key scientists, who claim to employ Bradford-Hill causal guidelines, yet fail to accept the pesticide-harm hypothesis, fall into errors of trimming the guidelines, requiring statistically-significant data, and ignoring semi-experimental evidence. However, the main scientists who accept the hypothesis appear to commit none of these errors. Although settling disagreement over the pesticide-harm hypothesis requires extensive analysis, this article suggests that at least some conflicts may arise because of questionable interpretations of the guidelines.