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We argue that the simplicity achieved is gained at a cost; dichotomization may create rather than avoid problems, notably a considerable loss of power and residual confounding. In addition, the use of a data\u2010derived \u2018optimal\u2019 cutpoint leads to serious bias. We illustrate the impact of dichotomization of continuous predictor variables using as a detailed case study a randomized trial in primary biliary cirrhosis. Dichotomization of continuous data is unnecessary for statistical analysis and in particular should not be applied to explanatory variables in regression models. Copyright \u00a9 2005 John Wiley &amp; Sons, Ltd.<\/jats:p>","DOI":"10.1002\/sim.2331","type":"journal-article","created":{"date-parts":[[2005,10,11]],"date-time":"2005-10-11T07:48:02Z","timestamp":1129016882000},"page":"127-141","source":"Crossref","is-referenced-by-count":2063,"title":["Dichotomizing continuous predictors in multiple regression: a bad idea"],"prefix":"10.1002","volume":"25","author":[{"given":"Patrick","family":"Royston","sequence":"first","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Douglas G.","family":"Altman","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Willi","family":"Sauerbrei","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"311","published-online":{"date-parts":[[2005,10,11]]},"reference":[{"key":"e_1_2_1_2_2","doi-asserted-by":"publisher","DOI":"10.1037\/0033-2909.113.1.181"},{"key":"e_1_2_1_3_2","doi-asserted-by":"publisher","DOI":"10.1097\/00001648-199507000-00002"},{"key":"e_1_2_1_4_2","volume-title":"Generalized Additive Models","author":"Hastie TJ","year":"1990"},{"key":"e_1_2_1_5_2","doi-asserted-by":"publisher","DOI":"10.2307\/2986270"},{"key":"e_1_2_1_6_2","doi-asserted-by":"publisher","DOI":"10.1016\/S0029-7844(96)00504-2"},{"key":"e_1_2_1_7_2","doi-asserted-by":"publisher","DOI":"10.1037\/1082-989X.7.1.19"},{"key":"e_1_2_1_8_2","doi-asserted-by":"publisher","DOI":"10.1509\/jmkr.40.3.366.19237"},{"key":"e_1_2_1_9_2","doi-asserted-by":"publisher","DOI":"10.1177\/014662168300700301"},{"key":"e_1_2_1_10_2","doi-asserted-by":"publisher","DOI":"10.1093\/jnci\/86.11.829"},{"key":"e_1_2_1_11_2","unstructured":"HarrellJrFE. 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