This design is also called a case-control study. Enter the number with low exposure in one row, and the number with high exposure in the other row. Then you would assess EMF exposure in all subjects. To perform a retrospective study of the EMF-leukemia link, you would recruit one group of subjects with leukemia and a control group that does not have leukemia but is otherwise similar.
As an example, let's consider how to conduct a cross-sectional study of the link between electromagnetic fields (EMF) and leukemia. In a cross-sectional study, you recruit a single group of subjects and then classify them by two criteria (row and column).
artery obstructed).Ĭontingency tables display data from these five kinds of studies: (If you’re wondering, SPSS will only do a Fisher’s Exact for a 2×2 table).Contingency tables summarize results where you compared two or more groups and the outcome is a categorical variable (such as disease vs. Great software if you can get access to it. Not all standard statistical software will do one for a 2×4 table, but it can be done. If you still find that your expected values are too low, use a Fisher’s Exact test. Often when the observed values are low, the totals are too, so they overlap a lot, but not always.Ģ. (The expected value for each cell is row total*column total/overall total). It is that the expected value in each cell is greater than 5. The assumption of the Chi-square test is not that the observed value in each cell is greater than 5. Is there any other test that I could use that overcomes the limitations of chi-square?ġ. I cannot run the chi-square test because most of the cells contain values less than five and a couple of them contain values of 0. I have to compare two sets of categorical data in a 2×4 table. This question comes up a lot, so I thought I’d share my answer. I was recently asked this question about Chi-square tests.
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