Chapter 7: Comparing Several Means

This chapter will examine whether or not the observed differences in the samples may be attributed to just the natural variability among sample means or whether a reason exists why the groups have different means in the population.

OVERVIEW

If by constructing histograms and calculating some basic descriptive statistics we have concluded that some differences are present in our groups of study, we now need to figure out whether the observed differences between the samples may be attributed to just the natural variability among sample means or whether we have reason to believe that the groups have different means in the population.

The null hypothesis says that in the population, the means of the groups are equal. That is, no difference exists in the average of our tested response. The alternative hypothesis is that a difference exists. The alternative hypothesis does not say which groups differ from one another. It just says that the groups are not all the same ” at least one of the groups differs from the others.