Cohen's D Calculator

Cohen's D is a standardized effect size measure that represents the difference between the means of two groups in terms of standard deviation units. It is calculated by dividing the difference between the means of two groups by the pooled standard deviation.

A positive Cohen's D indicates that the mean of one group is greater than the mean of the other group, while a negative Cohen's D value indicates the opposite.

To understand the calculation of Cohen's D for effect size, let's take the following data sets as an example:

• Data set .
• Data set .

You can calculate Cohen's D in four steps:

1. Calculate the means of datasets.

   The first step is to calculate the means, , and , of the two datasets. This can be calculated by dividing the sum of the dataset by the number of data points in the dataset, i.e.:

where and are the lengths of and , respectively. For our example, the means are and . Check out our mean calculator and average calculator to understand more about this calculation.

2. Compute the standard deviations of datasets.

   Now, compute the standard deviation, and , for both sampled data sets and . You can check out our standard deviation calculator to understand more about this calculation, but the formula is:

Thus, and .

3. Calculate the pooled standard deviation.

   Next, calculate the pooled standard deviation () using the formula:

For our example, .

4. Calculate Cohen's D.

   The last step is to calculate Cohen's D using the Cohen's D formula:

For our example, .