Statistical Sciences 2037A/B Lecture Notes - Odds Ratio, Aspirin, Relative Risk
15 Jan 2013
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Document Summary
Categorical variables are shown in contingency variables because they cover the contingency combinations for both variables. It is hard to make comparisons from contingency tables. We can calculate conditional percentages for the response variable. The rate is the number of individuals per hundred, percentage is rate/100. Proportion of the total and odds (involves the other category). 40% of 1000 carry a gene then the proportion is 0. 40. Odds = # with trait/# without trait to 1 . Proportion odds = p/1-p to 1 , p=proportion. The baseline risk is the risk without the treatment or behaviour. For the aspirin/heart attack example the baseline risk is the risk of a heart attack without taking aspirin. The baseline risk can be hard to find. The relative risk of an outcome for two categories of an explanatory variable is the ratio of risk for each category. Relative risk of one means the risk is the same for both options.
