STATS 250 Lecture Notes - Lecture 21: Mean Absolute Difference, Sample Size Determination, Standard Error
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STATS 250 Full Course Notes
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Recall there are two methods for conducting inference for the difference between two population means for independent samples the general (unpooled) case and the pooled. Both will result in a t test statistic, but the standard error used in the denominator differ as well as the degrees of freedom used for computing the p value using a t distribution. H0: 1 = 2 (or 1 - 2 = 0) versus ha: 1 2. H0: 1 = 2 versus ha: 1 > 2 versus ha: 1 < 2. We will focus on the pooled t-test overall. We will see a levene"s f test in spss output to help us assess if pooling is reasonable. If the sample standard deviations are similar, the assumption of common population variance is reasonable and the pooled procedure can be used. If the sample sizes happen to be the same, the pooled and unpooled standard errors are equal anyway.
