Base SAS 9.1.3 Procedures Guide - Acsu Buffalo

72 Chapter 2. The FREQ Procedure
These individual table results demonstrate the occasional problems with combining
information into one table and not accounting for information in other variables such
as Gender. Figure 2.5 contains the CMH results. There are three summary (CMH)
statistics; which one you use depends on whether your rows and/or columns have
an order in r × c tables. However, in the case of 2 × 2 tables, ordering does not
matter and all three statistics take the same value. The CMH statistic follows the chisquare
distribution under the hypothesis of no association, and here, it takes the value
4.0186 with 1 degree of freedom. The associated p-value is 0.0450, which indicates
a significant association at the α = 0.05 level.
Thus, when you adjust for the effect of gender in these data, there is an association
between internship and program enrollment. But, if you ignore gender, no association
is found. Note that the CMH option also produces other statistics, including estimates
and confidence limits for relative risk and odds ratios for 2×2 tables and the Breslow-
Day Test. These results are not displayed here.
Summary Statistics for Internship by Enrollment
Controlling for Gender
Cochran-Mantel-Haenszel Statistics (Based on Table Scores)
Statistic Alternative Hypothesis DF Value Prob
---------------------------------------------------------------
1 Nonzero Correlation 1 4.0186 0.0450
2 Row Mean Scores Differ 1 4.0186 0.0450
3 General Association 1 4.0186 0.0450
Total Sample Size = 223
Figure 2.5.
Test for the Hypothesis of No Association
Agreement Study Example
Medical researchers are interested in evaluating the efficacy of a new treatment for a
skin condition. Dermatologists from participating clinics were trained to conduct the
study and to evaluate the condition. After the training, two dermatologists examined
patients with the skin condition from a pilot study and rated the same patients. The
possible evaluations are terrible, poor, marginal, and clear. Table 2.2 contains the
data.