Welch's t-test
Computes the Welch's t-test statistic, the two-sample t-test version that does NOT assume equal variances. Unlike the classic Student's t-test, it doesn't pool the variances into a single value, which makes it more reliable when the two groups have different spreads — the default recommendation in modern statistics. The degrees of freedom come from the Welch-Satterthwaite equation, usually fractional. Enter the mean, standard deviation and size of each of the two groups.
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Welch's t-test
Computes the Welch's t-test statistic, the two-sample t-test version that does NOT assume equal variances. Unlike the classic Student's t-test, it doesn't pool the variances into a single value, which makes it more reliable when the two groups have different spreads — the default recommendation in modern statistics. The degrees of freedom come from the Welch-Satterthwaite equation, usually fractional. Enter the mean, standard deviation and size of each of the two groups.
The t-test that doesn't trust equal variances
The classic Student's t-test carries a fragile assumption: that the two groups compared have the same variance. When that doesn't hold, and it rarely does in practice, the test loses reliability. Welch's t-test fixes this so robustly that many statisticians argue for using it always, by default, instead of the classic one.
The difference is in how it treats the variances. Instead of pooling them into a single value, Welch keeps each one separate in computing the standard error. The price is that the degrees of freedom stop being a round number and come from the Welch-Satterthwaite equation, almost always fractional, reflecting the imbalance between the groups.
Enter the mean, standard deviation and size of each of the two groups. The tool returns the t-statistic and the Welch degrees of freedom. With those two numbers you consult the t-distribution to get the p-value and decide whether the difference between the means is statistically significant.
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The results provided by this tool are for general informational and educational purposes only and do not constitute professional, financial, medical, legal, tax or accounting advice. Always confirm important decisions with a qualified professional and official sources.