Where \(\bar x_1\) and \(\bar x_2\) are the two means, and \(s_{{\bar x_1} - {\bar x_2}}\) is an estimate of the Standard Error of the difference between the means:
\[\begin{align} t=\frac{\bar x_1-\bar x_2}{s_{{\bar x_1} - {\bar x_2}}} \end{align}\]
where:
\(p \approx 2\Pr(t_{n-1} \ge |t|)\),
\(n\) is the sample size,
\(s_{{\bar x_1} - {\bar x_2}}\) is computed as the Standard Error of \(d\),
the value for the \(i\)th observation is computed as \(d_i = x_{i1} - x_{i2}\) where \(x_1\), \(x_2\) are the observed values on the two variables.