Question 1

What is the difference between equal variance and Welch’s t-test?

Accepted Answer

Equal variance (pooled) assumes both groups have the same standard deviation. Welch’s t-test does not assume equal variances and uses the Welch–Satterthwaite formula for degrees of freedom, which is more robust when variances differ.

Question 2

How do you interpret Cohen’s d?

Accepted Answer

Cohen’s d indicates effect size: small (d < 0.2), medium (d ≈ 0.5), large (d > 0.8). Values above 0.8 are considered large effects.

Question 3

Can I use the paired t-test for unequal sample sizes?

Accepted Answer

No, paired t-test requires the same number of observations in both columns (paired data). Missing values should be excluded pairwise.

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