Combined variance (two groups, internal variances about own means) (Pooled variance: within-group spread plus between-group mean shift)
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Pooled variance: within-group spread plus between-group mean shift
What each symbol means
| Symbol | What it stands for |
|---|---|
| d_i | Deviation of group mean from pooled mean |
When to use this
σ_i² are variances within each group (divisor n_i convention must match problem).