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Effect size calculator
Enter the means, standard deviations and sample sizes for two groups. You get Cohen's d with a confidence interval, Hedges' g corrected for small samples, conversions to r and to an odds ratio, and the sentence to report it.
Cohen's bands were offered as rough conventions, not thresholds, and he said so himself. Whether an effect matters depends on your outcome, your field and what it costs to achieve — which is a judgement about the research, not the arithmetic.
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This calculator was checked by Hafiz Ahmad Tariq, Senior Biostatistician
In short
How do you calculate Cohen's d?
Cohen's d is the difference between two group means divided by their pooled standard deviation. Values around 0.2 are conventionally small, 0.5 medium and 0.8 large. In samples below about 50, Hedges' g should be reported instead, because d is biased upward when samples are small.
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