Term
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Definition
| chi-square models are skewed to the right; they are parameterized by their degrees of freedom and become less skewed with increasing degrees of freedom |
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Term
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Definition
| one element of a table corresponding to a specific row and a specific column; table cells can hold counts, percentages, or measurements on other variables or they can hold several values |
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| the chi-square statistic can be used to test whether the observed counts in a frequency distribution or contingency table match the counts we would expect according to some model, calculated as X^2 = sum of all (obs-exp)^2/exp; chi-square statistics differ in how expected counts are found, depending on the question asked |
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Term
| chi-square test of goodness-of-fit |
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Definition
| a test of whether the distribution of counts in one categorical variable matches the distribution predicted by a model is called a test of goodness-of-fit; in a chi-square goodness-of-fit test, the expected counts come from the predicting model; the test finds a P-value from a chi-square model with n-1 degrees of freedom, where n is the number of categories in the categorical variable |
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Term
| chi-square test of homogeneity |
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Definition
| a test comparing the distribution of counts for two or more groups on the same categorical variable; it finds expected counts based on the overall frequencies, adjusted for the totals in each group under the null hypothesis assumption that the distributions are the same for each group; we find a P-value from a chi-square distribution with (rows-1) x (columns-1) degrees of freedom where #rows gives the # of categories and #columns gives the number of independent groups |
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Term
| chi-square test of independence |
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Definition
| a test of whether 2 categorical variables are independent examines the distribution of counts for one group of individuals classified according to both variables; it finds expected counts by assuming that knowing the marginal totals tells us the cell frequencies assuming that there is no association between the variables; same calculation as test of homogeneity |
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Term
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Definition
| (observed - expected)^2 / expected |
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| the square root of the chi-square component for each cell of a two-way table; can show in a rejected test how the data deviates from the null model |
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Term
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Definition
| the square root of the chi-square component for each cell of a two-way table; can show in a rejected test how the data deviates from the null model |
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Term
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Definition
| each cell of a two-way table shows counts of individuals; one way classifies a sample according to a categorical variable; the other way can classify different groups of individuals according to the same variable or classify the same individuals according to a different categorical variable |
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Term
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Definition
| a two-way table that classifies individuals according to two categorical variables |
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