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We want to study the relationship between the exposure to second hand smoke, and the development of heart disease. what are the case and controls?
- case: people who have heart disease
- control: people who don't have heart disease
What are the steps in a case control study? (4)
- state your research question
- define your population
- choose cases then choose control
- compare the level of exposure in the case and control groups
What do you compare between the case and control group in a case control study?
the level of exposure
True or false: case control studies are recruited based on their exposure status
False, recruited based on their outcome status
Who are the controls in a case control study? (2)
- should not have disease or outcome
- should be at risk for getting the outcome
Where do controls come from in case control study? (5)
- disease registries
- neighborhood controls
- best friend controls
- general population controls
How can we make a comparison in case control studies?
What is odds ratio?
the odds of having the disease among the exposed, relative to the odds of having the disease among those who are not exposed
What is information bias in case control studies?
bias related to information collected about exposure and/or outcome
What is misclassification bias?
exposed subjects may be classified as non-exposed, or vice versa
How do we collect data on participants' past experiences? (4)
- ask them?
- survey them?
- look at medical records/pharmacy records
- physician exam
What is differential misclassification of exposure? What is an example?
- one group is more misclassified more frequently
- example: people in cases recall more accurately past exposures
What is non differential misclassification of exposure?
both study groups misclassified to the same degree
What is recall bias? (2)
- when people with a disease may search their mind a little harder than healthy controls
- cases may put more effort into trying to explain their disease
What might happen with recall bias?
odds ratio will be inflated!
How can you reduce potential for information bias? (4)
- blind interviewers to disease status of the participant and to study hypothesis
- train interviewers
- verify information with records
How to minimize recall bias? (4)
- structured questionnaires
- cohort study design
- pre-existing records
- carefully select controls in case control study
who do you collect for controls in case control studies?
the population at risk
What are the pros for case control studies? (5)
- good for rare outcomes
- can give results in short time period
- relatively inexpensive
- good when there is a long latency period between exposure and outcome
What are the cons for case control studies? (2)
- sampling bias (recall bias)
- not as efficient when the frequency of exposure is low (rare)
True or false: case control studies can yield measures of incidence
false, because we're looking at EXISTING cases (prevalence)
Why can't we use risks and risk ratios for a case control study? (2)
- can't report the risk of the outcome
- we choose among exposure and outcome
What does an odds ratio of one indicate?
no relationship between exposure and outcome
What does an odds ratio of less than one indicate?
means exposure reduced the odds
What does an odds ratio of more than one indicate?
exposure increases the odds
How does misclassification occur? (3)
- incomplete records
- participants difficulty with recall
- poor measurement tools
Will increasing the sample size reduce the potential for differential misclassification?
No it will not.