Cohen's d Calculator
Calculate signed Cohen’s d for two independent samples using the sample-size-weighted pooled standard deviation.
Formula
sₚ = √[((n₁−1)s₁²+(n₂−1)s₂²)/(n₁+n₂−2)]; d = (M₁−M₂)/sₚ.
Pooled SD ≈ sqrt((((20)-1)×(4)^2+((20)-1)×(4)^2)÷((20)+(20)-2)) · Cohen’s d ≈ ((12)-(10))÷(4)
How to use
- Enter both sample means.
- Enter sample standard deviations and sizes of at least 2.
- Read d and the pooled standard deviation.
Examples
- Means 12 and 10, both SDs 4 and both sizes 20 give d = 0.5.
Frequently asked questions
Which convention is used?
Independent-samples d with degrees-of-freedom-weighted pooling, as defined by Lakens. It is not paired-sample d.
What does the sign mean?
Positive means sample 1 has a higher mean. Reverse the samples to reverse the sign.
Is this Hedges’ g?
No bias correction is applied. Both standard deviations cannot be zero.
Sources
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