observational_studies - Author(s): Kerby Shedden, Ph.D.,...

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Unformatted text preview: Author(s): Kerby Shedden, Ph.D., 2010 License: Unless otherwise noted, this material is made available under the terms of the Creative Commons Attribution Share Alike 3.0 License: http://creativecommons.org/licenses/by-sa/3.0/ We have reviewed this material in accordance with U.S. Copyright Law and have tried to maximize your ability to use, share, and adapt it. The citation key on the fol owing slide provides information about how you may share and adapt this material. Copyright holders of content included in this material should contact open.michigan@umich.edu with any questions, corrections, or clarification regarding the use of content. For more information about how to cite these materials visit http://open.umich.edu/privacy-and-terms-use. Any medical information in this material is intended to inform and educate and is not a tool for self-diagnosis or a replacement for medical evaluation, advice, diagnosis or treatment by a healthcare professional. Please speak to your physician if you have questions about your medical condition. Viewer discretion is advised : Some medical content is graphic and may not be suitable for al viewers. 1 / 44 Observational Studies and Experiments Kerby Shedden Department of Statistics, University of Michigan April 8, 2011 2 / 44 Comparative studies The goal of a comparative study is to estimate the difference in some characteristic between groups. Here are some examples of comparative studies: Comparisons within populations A specific medical treatment is compared to giving no treatment, or a new treatment is compared to the current standard treatment. Comparisons over time The number of US highway fatalities in 2000-2005 is compared to the number of US highway fatalities in 1995-1999. 3 / 44 Comparative studies Examples of comparative studies (continued): Comparisons across populations The number of highway fatalities per kilometer driven in the US is compared to the number of highway fatalities per kilometer driven in Canada. Comparisons across levels of a continuous factor Rates of home foreclosure are compared based on the amount of downpayment paid. 4 / 44 Non-comparative studies A non-comparative study typically aims to estimate some quantity, e.g. the proportion of US children without health insurance but the estimate is not immediately compared to anything. 5 / 44 Terminology The characteristic being compared (i.e. successful treatment response, traffic fatalities, home foreclosure) is called the outcome variable (sometimes the response variable or dependent variable ). Sometimes the treatment group or factor is called the independent variable . Any additional variables measured at or before the time of treatment are called covariates . Any variables measured after treatment are outcomes ....
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observational_studies - Author(s): Kerby Shedden, Ph.D.,...

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