Statistical Analysis with R Essentials For Dummies

Chapter 11

Testing More Than Two Samples

IN THIS CHAPTER

Analyzing variance

Planning comparisons

Working with repeated measures

Statistics would be limited if you could only make inferences about one or two samples. In this chapter, I discuss the procedures for testing hypotheses about three or more samples. I show what to do when samples are independent of one another, and what to do when they’re not. In both cases, I discuss what to do after you test the hypotheses. I also discuss R functions that do the work for you.

Testing More Than Two

Imagine this situation. Your company asks you to evaluate three different methods for training its employees to do a particular job. You randomly assign 30 employees to one of the three methods. Your plan is to train them, test them, tabulate the results, and make some conclusions. Before you can finish the study, three people leave the company — one from the Method 1 group and two from the Method 3 group.

Table 11-1 shows the data.

TABLE 11-1 Data from Three Training Methods

Method 1	Method 2	Method 3
95	83	68
91	89	75
89	85	79
90	89	74
99	81	75
88	89	81
96	90	73
98	82	77
95	84
80
Mean	93.44	85.20 ...