Basic Analysis and Graphing - SAS

200 Performing Contingency Analysis Chapter 6
Cochran Armitage Trend Test
Related Information
• “Example of the Measures of Association Option” on page 211
Cochran Armitage Trend Test
This Cochran Armitage Trend tests for trends in binomial proportions across the levels of a single variable.
This test is appropriate only when one variable has two levels and the other variable is ordinal. The two-level
variable represents the response, and the other represents an explanatory variable with ordered levels. The
null hypothesis is the hypothesis of no trend, which means that the binomial proportion is the same for all
levels of the explanatory variable.
The test statistic and p-values given in this section are approximate. An exact version of the trend test is
available. See “Exact Test” on page 200.
Related Information
• “Example of the Cochran Armitage Trend Test” on page 211
Exact Test
The following table describes the exact versions of three of the tests available in the Contingency platform.
Fisher’s Exact Test
Performs Fisher’s Exact test for an r x c table. This is a test
for association between two variables. Fisher’s exact test
assumes that the row and column totals are fixed, and uses
the hypergeometric distribution to compute probabilities.
This test does not depend on any large-sample
distribution assumptions. This means it is appropriate for
situations where the Likelihood Ratio and Pearson tests
become less reliable, like for small sample sizes or sparse
tables.
The report includes the following information:
Table Probability (P) gives the probability for the
observed table. This is not the p-value for the test.
Two-sided Prob ≤ P
test.
gives the p-value for the two-sided
For 2x2 tables, the Fisher’s Exact test is automatically
performed. See “Tests” on page 193.