Chapter Summary

Two-sample t-tests and confidence intervals for the difference between means allow us to compare results obtained from two samples. For hand calculations, pooled variances estimators simplify the calculations but require adding the assumption of equal variances in the populations. Two-sample z-tests and confidence intervals for proportions proceed in a similar way. Experiments provide the ideal data for such comparisons. In an experiment, subjects from a sample are randomly assigned to treatments defined by levels of an experimental factor. This randomization avoids confounding, which introduces the possibility of lurking variables. Paired comparisons focus on the differences between corresponding subjects by ruling out other ...

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