Introduction to the Chi Square Test of Independence (1 of 2)

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Contingency tables are used to examine the relationship between subjects' scores on two qualitative or categorical variables. For example, consider the hypothetical experiment on the effectiveness of early childhood intervention programs described in another section. In the experimental group, 73 of 85 students graduated from high school. In the control group, only 43 of 82 students graduated. These data are depicted in the contingency table shown below.

	Graduated	Failed to Graduate	Total
Experimental	73	12	85
Control	43	39	82
Total	116	51	167

The cell entries are cell frequencies. The top left cell with a "73" in it means that 73 subjects in the experimental condition went on to graduate from high school; 12 subjects in the experimental condition did not. The table shows that subjects in the experimental condition were more likely to graduate than were subjects in the control condition. Thus, the column a subject is in (graduated or failed to graduate) is contingent upon (depends on) the row the subject is in (experimental or control condition).