EHS 260 Lecture Notes - Lecture 17: Absolute Difference, Relative Risk, Odds Ratio
18 Jun 2018
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Risk difference
Also called excess risk
The absolute difference in rates of occurrence between groups of individuals who have and who
have not been exposed to the factor of interest
Relative risk
Also called risk ratio
The ratio of the risk of occurrence among exposed people to that among unexposed
It measures the strength of an association.
Relative risk
Ex.
Let’s assume that the incidence of stroke is 17.7 per 100,000person-years among non-
smokers and 49.6 per 100,000 person years among smokers.
The relative risk of stroke in smokers compared with non-smokers is therefore 2.8
(49.6/17.7)
In other words, smokers are 2.8 times more likely to have a stroke than non-smokers
When dealing with exposures that are associated with a decreased risk of disease (often the case for PA)
researchers sometimes take the unexposed group (the inactive group) as the reference category.
Risk difference
Also called excess risk
The absolute difference in rates of occurrence between groups of individuals who have and who
have not been exposed to the factor of interest
Relative risk
Also called risk ratio
The ratio of the risk of occurrence among exposed people to that among unexposed
It measures the strength of an association.
Ex.
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
When dealing with exposures that are associated with a decreased risk of disease (often the case for pa) researchers sometimes take the unexposed group (the inactive group) as the reference category. The absolute difference in rates of occurrence between groups of individuals who have and who have not been exposed to the factor of interest. The ratio of the risk of occurrence among exposed people to that among unexposed. It measures the strength of an association. Let"s assume that the incidence of stroke is 17. 7 per 100,000person-years among non- smokers and 49. 6 per 100,000 person years among smokers. The relative risk of stroke in smokers compared with non-smokers is therefore 2. 8 (49. 6/17. 7) In other words, smokers are 2. 8 times more likely to have a stroke than non-smokers. Example: smokers vs. non-smokers sedentary people vs. physically active people. Odds ratio (similar to relative risk, used in many case-control studies); Comparison of disease occurrence between exposed and unexposed groups.
