The RxC chi-square test can be used to analyze discontinuous (frequency) data as in the Fisher s exact or 2x2 chi-square tests. However, in the RxC test (R = row, C = Column) we wish to compare three or more sets of data. An example would be comparison of the incidence of tumors among mice on three or more oral dosage levels. We can consider the data as positive (tumors) or negative (no tumors). The expected frequency for any box is equal to (row total)(column total)/(A/,otal). [Pg.912]

Here you can still use the Pearson chi-square test as shown in the 2x2 table example as long as your response variable is nominal and merely descriptive. If your response variable is ordinal, meaning that it is an ordered sequence, and you can use a parametric test, then you should use the Mantel-Haenszel test statistic for parametric tests of association. For instance, if in our previous example the variable called headache was coded as a 2 when the patient experienced extreme headache, a 1 if mild headache, and a 0 if no headache, then headache would be an ordinal variable. You can get the Mantel-Haenszel /pvalue by running the following SAS code [Pg.252]

A similar pattern emerged with contingency chi-square tests (Chapter 16). The simplest 2x2 tables led to clear unambiguous conclusions while results from larger tables were much less easily interpreted. [Pg.278]

Though Fisher s Exact Test is preferable for analysis of most 2x2 contingency tables in toxicology, the chi square test is still widely used and is preferable in a few unusual situations (particularly if cell sizes are large yet only limited computational support is available). [Pg.911]

Typically, comparison of incidences of any one type of lesion between controls and treated animals are made using the multiple 2x2 chi square test or Fisher s exact test with a modification of the numbers of animals as the denominators. Too often, experimenters exclude from consideration all those animals (in both groups) that died prior to the first animals being found with a lesion at that site. [Pg.962]

The rule of thumb for the use of Fisher s exact test is based on the expected frequencies in the 2x2 contingency table each of these need to be at least five for the chi-square test to be used. In the example, the expected frequencies in each of the two cells corresponding to success are 3.5, signalling that Fisher s exact test should be used. [Pg.72]

If the normal approximation to the binomial distribution is valid (that is, not more than 20% of expected cell counts are less than 5) for drug therapy and symptom of headache, then you can use the Pearson chi-square test to test for a difference in proportions. To get the Pearson chi-square / -value for the preceding 2x2 table, you run SAS code like the following [Pg.251]

Statistical analysis is performed on all parameters in the study. Its most fundamental objective is to determine whether administration of the test agent results in an increase in tumor incidence rates as compared to those in unexposed controls. Various statistical methods can be used. Tests for increased tumor occurrence rates between dosages may be based on pair-wise comparisons, such as the Chi-square test for 2x2 tables, the Fisher s exact test, or the Cochan-Armitage test. These tests are most appropriate when survival rates do not differ appreciably in the various dose groups. [Pg.435]

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