Two-Sample t-Test
Welch's two-sample t-statistic, Welch-Satterthwaite df, p-value, significance flag, and mean difference, reusing the bundled Student-t CDF.
Formula and source
t = (m1-m2)/sqrt(s1^2/n1 + s2^2/n2); Welch df = (s1^2/n1 + s2^2/n2)^2 / [ (s1^2/n1)^2/(n1-1) + (s2^2/n2)^2/(n2-1) ]; p from the Student-t CDF.
Per OpenIntro Statistics Chapter 7 (inference for numerical data, Welch's t) and the Welch-Satterthwaite df, by name; the t-CDF reuses the bundled special-function helper.
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