Measures of Association Flashcards
What are measures of association and what do they do?
They provide a mathematical assessment of the relationship between a given exposure and the outcome of interest. They determine if there is an association and measure the strength of said association.
What happens if the number of subjects in the groups isn’t the same, when looking at association?
You need to use measures of dz occurrence, such as prevalence, incidence, and odds, to calculate measures of association.
When would you use an odds ratio?
In a retrospective study (cross-sectional studies or case control studies) when comparing exposure in outcome groups.
When would you use relative risk or attributable risk?
In prospective studies. Would use attributable risk in prospective cohort studies and clinical trials. Use this when comparing outcomes in exposure groups
When would you use prevalence ratio?
When comparing outcomes in exposure groups, using retrospective studies.
What is odds used to measure?
measures the exposure in the diseased and non-diseased groups. It is the ratio of the number exposed to the number not exposed.
What is the odds of exposure if you’ve got 10 diseased animal and only 3 were exposed?
3/7
What is the odds ratio?
the odds of exposure in the diseased group, to the odds of exposure in the non-diseased group.
What does the OR tell you?
if there is an association and the magnitude of said association.
If the OR is 1, what does that tell you?
No association.
If the OR is >1, what does that tell you?
positive association, possibly causal.
If the OR is <1 what does that tell you?
negative association, possibly protective.
Using the following table, what would be the formula for the odds ratio?
ad/bc
When are odds a great approximation of the risk?
when it comes to rare dz outcomes.
Which observational study design compares exposed to non-exposed study subjects?
Cohort
what is incidence?
the measure used to compare the amount of dz that occurs in the exposed and unexposed groups in prospective studies.
What is the incidence rate?
The number of new cases at the end of the study, divided by the animal time at risk.
What is the relative risk?
It is used to compare the risk of dz that occurs in the exposed and unexposed groups. It is the ratio of incidence of disease in the exposed to the incidence of dz in the unexposed.1
If the relative risk = 1, what does it mean?
means there is no association.
Using the following table, what is the relative risk formula?
(a/(a+b))/(c/(c+d))
What does the attributable risk tell you?
the amount of dz you would prevent if you removed exposure.
Is attributable risk used to quantify association?
No. It is used to set priorities in dz control programs.
What is the formula for AR?
Riskexposed-Riskunexposed/Riskexposed
What is prevalence?
the measure used to compare the amount of dz that occurred in the exposed and unexposed groups in retrospective studies.
Why is prevalence used?
because the disease has already occurred when the study has begun (in cases of retrospective studies)
What is the formula to calculate prevalence ratio?
prevalence of dz in exposed/prevalence of dz in unexposed
What measure of dz is used in case control studies?
odds
What measure of dz is used in prospective cohort studies?
incidence
What measure of dz is used in clinical trials?
incidence
