ABSTRACT
The 2 × 2 contingency table is very widely used to display the comparison between two independently sampled proportions or the association between two binary variables. Table 7.1 shows three representations of the 2 × 2 contingency table used to compare a binary outcome variable between two independent groups 1 and 2. In this chapter, and also in Chapter 10 which deals with the ratio of independent proportions, we are assuming that the column totals, m and n, are fixed. For example, the data could come from a randomised trial in which m subjects are allocated to treatment 1 and n subjects are allocated to treatment 2. In statistical parlance, inferences are conditional on the two marginal totals, m and n. This contrasts with the situation in a cross-sectional study, in which often only the table total is fixed. In Chapter 8 we consider a very different 2 × 2 table representing paired binary data.
