Making Sense of Statistics
Different kinds of studies use different statistical methods. Even if you hate statistics with a passion, knowing the statistical tests associated witheach study type can help you do a quick evaluation. If a particular study uses an inappropriate statistical method, the results might not be valid and to read further might be a waste of time.
Unfortunately there are many synonyms for the different types of studies and it can take a few minutes to find out the type of study ......
Effect size (ES) is a name given to a family of indices that can measure , for example, the magnitude of a treatment effects
The Incidence Ratio is one kind of effect size measure.
There is more than one formula in use. This site explains several. The explanations imply a knowledge of statistics.