Comparing Two Sample Means

Abstract

Up to now we have concentrated on single batches of numbers and on using single batches of numbers as samples for purposes of making inferences about the populations from which they were selected. The principles discussed in Chapters 7–11, however, can also be applied to the task of comparing batches, which we began to explore in Chapter 4. Figure 12.1 compares two batches of numbers. These batches are the areas (in square meters) of house floors for two periods (Formative and Classic). After careful consideration of possible sources of bias we decide to work with these two batches as if they were random samples, taking each as a sample of house floors for its period. The sample for the Formative period consists of 32 house floors, and the sample for the Classic period consists of 52 house floors. We begin to explore the two samples with a back-to-back stem-and-leaf plot at the left in Fig. 12.1. This plot reveals that both samples are single peaked and symmetrical enough that the mean would be a useful index of their levels. Neither is a perfect single-peaked and symmetrical shape, but both are quite as single peaked and symmetrical as one has any right to expect in relatively small batches of numbers like this.