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Statistics vocabulary · Reporting Results

Effect size

Meaning in statistics, with examples

nounCommon term

In statistics, effect size means: A number that shows how large a difference or relationship is, independently of sample size, such as Cohen's d, a correlation coefficient or an odds ratio.

In Turkish: etki büyüklüğü, etki değeri

How it is used

Journals that follow APA style expect effect sizes next to p-values, because a p-value only says whether an effect is likely to exist. Cohen's rough benchmarks for d are 0.2 (small), 0.5 (medium) and 0.8 (large). Effect sizes are also needed for power analysis and meta-analysis.

Example sentences

  1. The effect size was small (d = 0.21), even though the result was statistically significant.

  2. Please add effect sizes and confidence intervals to Table 3.

Common collocations

  • report the effect size
  • small effect size
  • Cohen's d
  • standardised effect size
  • effect size estimate
  • statistical significanceThe conclusion that a result is unlikely to be due to chance alone, judged by comparing the p-value with a chosen significance level such as 0.05.
  • p-valueThe probability of getting a result at least as extreme as the one observed if the null hypothesis were true; a small value means the data would be surprising under the null.
  • statistical powerThe probability that a test will detect an effect when a real effect of a given size exists; it equals one minus the probability of a Type II error.
  • sample sizeThe number of observations or participants included in a study, usually written as n (or N for the total).

This word in other fields

The same English word can have a different meaning in another field:

More terms: Reporting Results

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