Introduction to Statistics and Quantitative Research Methods

What if there is an effect?
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Odds Ratio (OR) is a way of comparing whether the probability of
a certain event is the same for two groups.
Used for cross-sectional studies, case control trials, and
retrospective trials.
In case control studies you can't estimate the rate of disease
among study subjects because subjects selected according to
disease/no disease. So, you can't take the rate of disease in both
populations (in order to calculate RR).
OR is the comparison between the odds of exposure among
cases to the odds of exposure among controls.
Odds are same as betting odds. Example: if you have a 1 in 3
chance of winning a draw, your odds are 1:2.
To calculate OR, take the odds of exposure (cases)/odds of
exposure (controls).
E.g. Smokers are 2.3 times more likely to develop lung cancer
than non-smokers.