In this chapter we will be looking at ways of determining whether the differences between the distributions of two variables are statistically significant. Thus, for example, when analysing data we may wish to know the answers to some of the following kinds of questions: Is the proportion of black to white workers the same among men as it is among women? Do women workers earn less than their male counterparts? Does job satisfaction change from one month to the next? Do the scores in one treatment group differ from those in another?