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Biostatistics

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12.4 TESTS OF INDEPENDENCE 623<br />

Computer Analysis The computer may be used to advantage in calculating X 2 for<br />

tests of independence and tests of homogeneity. Figure 12.4.1 shows the procedure and<br />

printout for Example 12.4.1 when the MINITAB program for computing X 2 from<br />

contingency tables is used. The data were entered into MINITAB Columns 1 and 2,<br />

corresponding to the columns of Table 12.4.3.<br />

We may use SAS ® to obtain an analysis and printout of contingency table data by<br />

using the PROC FREQ statement. Figure 12.4.2 shows a partial SAS ® printout reflecting<br />

the analysis of the data of Example 12.4.1.<br />

Data:<br />

C1: 260 15 7<br />

C2: 299 41 14<br />

Dialog Box:<br />

Session command:<br />

Stat Tables Chi-square Test MTB > CHISQUARE C1-C3<br />

Type C1-C2 in Columns containing the table.<br />

Click OK.<br />

Output:<br />

Chi-Square Test: C1, C2<br />

Expected counts are printed below observed counts<br />

C1 C2 Total<br />

1 260 299 559<br />

247.86 311.14<br />

2 15 41 56<br />

24.83 31.17<br />

3 7 14 21<br />

9.31 11.69<br />

Total 282 354 636<br />

Chi-Sq = 0.595 + 0.474 +<br />

3.892 + 3.100 +<br />

0.574 + 0.457 = 9.091<br />

DF = 2, P-Value = 0.011<br />

FIGURE 12.4.1 MINITAB procedure and output for chi-square analysis of data in Table 12.4.3.

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