Is relative risk an approximation of odds ratio?
The relative risk of one group compared with another is simply the ratio of the risks in the two groups. When the risks (or odds) in the two groups being compared are both small (say less than 20%) then the odds will approximate to the risks and the odds ratio will approximate to the relative risk.
Can you calculate relative risk in a case-control study?
In a case-control study, you cannot measure incidence, because you start with diseased people and non-diseased people, so you cannot calculate relative risk. Case-control studies are particularly useful when the outcome is rare is uncommon in both exposed and non-exposed people.
What does the odds ratio estimate in a case-control study?
The odds ratio is the “measure of association” for a case-control study. It quantifies the relationship between an exposure (such as eating a food or attending an event) and a disease in a case-control study.
How is relative risk measured?
A risk ratio (RR), also called relative risk, compares the risk of a health event (disease, injury, risk factor, or death) among one group with the risk among another group. It does so by dividing the risk (incidence proportion, attack rate) in group 1 by the risk (incidence proportion, attack rate) in group 2.
When to use odds ratio and relative risk?
For “incidence density” case-control studies, the odds ratio equals the relative risk when the estimate of exposure in the comparison group can be considered to be an estimate of the overall probability of exposure in the population at risk.
How is the odds ratio used in case control?
The odds ratio from a case-control study of the “cumulative-incidence” type can be used as an estimate of the relative risk of a disease attributable to exposure to an agent only when the incidence of the disease is low. The odds ratio can be modified to obtain an accurate estimate of the relative r …
How is relative risk determined in a cohort study?
Relative risk can be directly determined in a cohort study by calculating a risk ratio (RR). In case-control studies, and in cohort studies in which the outcome occurs in less than 10% of the unexposed population, the OR provides a reasonable approximation of the RR.
Can you calculate incidence in a case control study?
Key Concept: In a study that is designed and conducted as a case-control study, you cannot calculate incidence. Therefore, you cannot calculate risk ratio or risk difference. You can only calculate an odds ratio. However, in certain situations a case-control study is the only feasible study design.