# Tests of Differences between Means, Independent Groups, Standard Deviation
Estimated (3 of 8)

The estimated standard error,

, is computed assuming that the
variances in the two populations are

equal. If the two sample sizes are equal (n

_{1} =
n

_{2}) then the population variance σ² (it is
the same in both populations) is estimated by using the following
formula:

where MSE (which stands
for mean square error) is an estimate of
σ².
Once MSE is calculated,

can be computed as follows:

where n = n

_{1} = n

_{2}. This formula is derived
from the formula for the standard error of the difference between
means when the variance is

known.