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Just a note

t   =   (1 - 2) - (μ1 - μ2)
[ (n1 - 1)v1 + (n2 - 1)v2 ]( n1 + n2 )
n1 + n2 - 2 n1n2


  • t is the t-statistic; under the null hypothesis t is a random quantile of the t-distribution with (n1 + n2 - 2) degrees of freedom,
  • 1 and 2 are the two sample means , and μ1 and μ2 are the two population means,
  • sD is the estimated standard error of the difference between the means,
  • n1 & n2 are the number of observations in each sample,
  • v1 and v2 are the two sample variances.