Case Control Studies Flashcards
Cases that present are compared with one or more _______
Controls
- comparands: animals without the disease
Case control studies are ______
Retrospective
- compare frequency of occurrence of exposures/risk factors
- look at multiple risk factors to detect which ones are more or less seen in cases, and may be causal
- quickly done with low cost
Can case control studies be done to study rare or infrequent diseases?
Yes!
What is the measure of association for a cohort study?
Relative risk
- risk of disease in exposed/risk of disease in unexposed
What is the measure of association for a case control study?
Odds ratio
- odds of exposure in cases compared to odds of exposure in non-cases
Both, odds ratio and relative risk, measure ______
Strength of association between exposure and disease
What is the probability of an event occurring to the probability of the event not occurring?
Odds
Odds ratio and relative risk are pretty close when the disease is ______
Rare
Could odds ratio be used as the measure of association in cohort studies?
Yes, but relative risk is easier to communicate
Odds of exposure within cases
Disease present = number exposed/number unexposed
How to describe odds ratio?
The odds of exposure in the cases is ____, compared to the odds of exposure in non-cases
- the odds of exposure in cases is ____ times that of non-cases
Cross product ratio
Way to calculate odds ratio
- (ad)/(bc)
Odds ratio > 1 indicates
An increased risk of exposure to new cases
Odds ratio = 1 indicates
There is no increased risk
- no relationship between being a case and being exposed
Odds ratio < 1 indicates
Sparing effect
Can odds ratio go below zero?
No! It could theoretically go to infinity
- the bigger the number, the stronger the relationship
Odds ratio approximates relative risk if disease is _______
Rare in population (usually thought as <10%)
Can relative risk be used in case control studies?
No
Which study: OR is measure of association and OR estimates risk of exposure in cases compared to exposure in controls?
Case control
Which study: RR is effect measure, RR estimates risk of disease in exposed, compared to risk of disease in non-exposed
Cohort
Factor A occurs before disease X
Temporal relationship
- factor A causes disease X
Factor A is present very often in cases, and not in controls
Strength of association
- factor A causes disease X
Based on what is known, factor A could cause disease X
Biological plausibility
- factor A causes disease X
What are 7 conditions that would cause factor A causing disease X?
- temporal relationship
- strength of association
- biological plausibility
- dose response relationship
- consistency of multiple studies
- rule out other possible causes
- reversible associations
Cross sectional
A population of animals is sampled at a specific point in time
- snapshot of population
- prevalence study
- asses absolute risks in the population
With a cross sectional study, each animal is classified according to _____
Status of outcome and risk factor, simultaneously, at the time of the snapshot
Are temporal relationships established with a cross sectional study?
No, difficult to establish
- look at strength of association of risk factor and outcome