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  "body": "\n## Summary\n\nA contingency table counts how many observations fall into each combination of categories of two or more categorical variables.\nIt is the basic form of data for studying the association between categorical variables.\nThe chi-squared test and [[Fisher's exact test|J6JP5CJNPX]] test independence of the variables from such a table.\nLarger tables are analysed with log-linear models.\n\n## Explanations\n\n### L1 human\n\nAsk $100$ people whether they smoke and whether they exercise.\nWrite the answers in a table with two rows, smoker and non-smoker, and two columns, exercises and does not.\nEach cell holds the number of people with that pair of answers, and the four numbers add up to $100$.\nComparing the rows shows whether smoking and exercise seem related.\n",
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