Using the contingency chi-square test to compare observed proportions

1 Using the contingency chi-square test to compare observed proportions 

1 Expulsion rates of IUDs - an example of a contingency table 

The results obtained can be expressed in a so-called contingency table as in Tablel6.1. The characteristic feature of a contingency table is that both the columns and rows are based on categorizations. Here, the columns are based on the category of IUD used and the rows are based on outcomes, which are also categorized. 

A table where the columns and rows are based upon categorization. 

Since both the columns and rows of a contingency table are formed on the basis of categorizations, the table could be re-oriented so that the two different devices form the rows and the expelled/non-expelled categories form the columns. There is no absolute rule about how such tables should be laid out, but in the author s experience, they are more intuitive if the independent factor is used as the columns and the dependent as the rows. This is what has been done above (expulsion may depend upon device design, but not vice versa). In some tables the two forms of categorization, though potentially associated, may not have any obvious dependent relationship and the table could equally well be presented in either orientation. 

---

USING THE CONTINGENCY CHI-SQUARE TEST TO COMPARE OBSERVED PROPORTIONS 211... 

---