When to use Welch's test

Welch's t-test compares the means of two independent groups without assuming their variances are equal.

That makes it a safer default than the pooled two-sample t-test when the spread of one group may be noticeably different from the other.

The result panel combines the p-value, degrees of freedom, and confidence interval so the test outcome is easier to interpret quickly.

Reading the output

  • If the p-value is below your chosen alpha, reject the null hypothesis of equal means.
  • The confidence interval summarizes plausible values for mu1mu2mu_1-mu_2.
  • Welch's degrees of freedom are approximate, so they are usually not whole numbers.