Case Control Studies Flashcards
What are the fundamentals of case control studies? [4]
Identify individuals with a disease (cases)
Identify `similar’ individuals without the disease (controls)
Determine previous exposure
Relate information on exposure to disease
Where do you source cases [3] and controls [3]
Cases:
* Want representative of all people with the disease of interest
* Could be incident cases from disease registry
* Could be hospital based recruitment but this may give a biased sample
Controls:
* same population as cases
* If hospital based ensure the reason for being in hospital not also related to exposure of interest
* Usually more than one control per case
What is undermatching? [1]
Give an example [1]
What is overmatching? [1]
Give an example [1]
Undermatching: Cases and controls aren’t similar enough
* don’t match on age cases may be older and therefore more likely to smoke than controls.
Overmatching: Cases and controls may be too similar
* Eg if choose siblings may not differ in exposure of interest, for example parental smoking
Name 4 causes of bias in case control studies
Recall bias
* Cases may remember more than controls
Reverse causality
* Has disease caused changes in recent exposures
Selection of cases
* Are they representative of all people with the disease
Selection of controls
* Are they representative of all people without the disease
* Are they similar to the cases
Describe structure of a nested case control study [2]
“Prepared” the case control studies: collected e.g. blood samples from a large population.
These are frozen and then waited to see who gets the disease
.
Nested case-control studies are good for assessing what? [1]
Useful for biomarkers studies where biomarker is expensive to measure
I want to investigate a risk factor for a rare disease. Which should you use?
Why?
Cohort
Case control
Case control
If a disease is extremely rare a cohort study may have to be impractically large to get enough people with the disease
I want to investigate if a rare exposure is associated with a disease ? Which should I use and why?
Cohort
Case control
Cohort
If an exposure is rare there may be too few people exposed in a case-control study to be able to draw conclusions
Why cant you calculate relative risk of of a case control study?
Do not know risk of the disease (as you have started with cases with the disease)
Whata can you assess instead of relative risk in a case control study?
Use Odds Ratios = odds exposure in case / odds exposure in controls
State 4 causes of bias in case control studies [4]
- Recall bias: cases may remember more than controls. If you have a disease and are being asked about previous exposures, you will have more thought into this than the controls will.
- Reverse causality: has disease caused changes in recent exposures?
- Selection of cases: are they representative of all people with the disease?
- Selection of controls: are they representative of all people without the disease and are they similar to the cases?
How effective is odds ratio for an estimate of relative risk if a disease is rare? [1]
If the disease is RARE the odds ratio is a good estimate of the relative risk
Interpret this odds ratio [1]
Babies who died were twice as likely to have been put on their sides rather than their backs compared to babies who did not die
How can you assess for confounding variables in controsl that weren’t matched for? [1]
logistic regression
How can you assess for confounding variables in controsl that weren’t matched for? [1]
logistic regression
How do you calculate attributable proportion in a case control study?
Calculate the attributable proportion for this data?
Place the following in order of most to least likely to have bias
Case-control
Cohort
Clinical trial
Cross-sectional survey
Place the following in order of most to least likely to have a risk of confounding factors
Case-control
Cohort
Clinical trial
Cross-sectional survey
Place the following in order the strength of proof in causility in the following?
Case-control
Cohort
Clinical trial
Cross-sectional survey
