**Unformatted text preview: **1 – μ 2 It clusters around a mean of 0, as predicted by H We calculate the standard error of the difference between means Calculating the standard error o There are 2 different formulas to use, depending on whether σ 1 2 (population variance for group 1) = σ 2 2 (population variance for group 2) o We will use only one – assume that σ 1 2 ≠ σ 2 2 Unequal standard deviations o For unequal population variances: σ 1 - 2 = ( (s 1 2 / n 1-1) + (s 2 2 / n 2-1)) o The formula for t is: t obt =( 1- 2 )/ ( (s 1 2 / n 1-1) + (s 2 2 / n 2-1)) Degrees of freedom o For unequal standard deviations, it can be more complicated o DF=n 1 +n 2-2 is still a good estimate (contrary to what your book says)...

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- Spring '09
- Kupchick
- Statistics, Standard Deviation, Variance, Ronald Fisher