Case Control Studies Flashcards
How are case control studies carried out
Identify cases -> identify similar individuals without disease /controls -> determine previous exposure -> relate exposure and disease info
Where can cases for case control studies be found
Disease registry
Hospital recruitment
Is there usually more cases or more controls in a case control study
Controls
Why are patients and controls matched
Decr impact of confounders
Why can overmatching effect results negatively
Case and control may not differ in exposure of interest, eg siblings both effected by parental smoking
Types of bias in case control studies
Recall bias
Reverse causality
Selection of cases
Selection of controls
Recall bias
differences in the accuracy or completeness of the recollections retrieved by study participants regarding events or experiences from the past.
Reverse causality
direction of cause-and-effect contrary to a common presumption or to a two-way causal relationship
Disease causes changes in recent exposures
Cohort study case control study difference
cohort study is concerned with frequency of disease in exposed and non-exposed individuals, the case-control study is concerned with the frequency and amount of exposure in subjects with a specific disease (cases) and people without the disease (controls)
Are cohort studies or case control studies better for rare diseases
Case control
How does a Nested case control study differ from a regular case control study
Cohort defined before identifying is individuals have disease or not in nested case control
Nested case controls require samples to be stored
Is a cohort study or case control study better for a rare exposure
Cohort
Are case control studies or cohort studies quicker
Case control
Is recall bias more of a problem in cohort or case control studies
Case control
Why can relative risk not be calculated in a case control study
Number with and without disease selected
What type of disease is relative risk approximately equal to odds ratio in
Rare disease
How is odds ratio calculated
Odds exposure in cases / odds exposure in controls
How can confounding variables be adjusted for in cohort studies
Logistic regression
Can risk be calculated in a case control study
No
How is absolute excess risk calculated
Risk in exposed - risk in unexposed
What does incidence in population attributable to exposure/ incidence in population calculate
Attributable proportion
How are incidence in population and incidence in population attributable to exposure calculated
Attributable to exposure - proportion exposed (relative risk-1)
Total incidence - 1+proportion exposed (relative risk - 1)
Cross sectional study
Measure existing disease and current exposure and 1 point in time
What are cross sectional studies used to assess
Exposure that won’t change - eg sex
Prevalence rate
Exposure rate
Disadvantages of cross sectional studies
Not useful for rare diseases
Not useful for diseases with short duration
Bias if responders and non responders differ
Can’t assess causality
Why can causality not be assessed in a cross sectional study
No follow up
What is usually used to collect data in a cross sectional study
Questionnaire
Which studies have the highest risk of bias and confounding out of clinical trials, cohort studies, case control studies, and cross sectional studies
Cross sectional -> case control -> cohort -> clinical trial
Most to least likely to have bias and confounding
Which studies give the strongest proof of causality out of clinical trial, cohort studies, case control studies, and cross sectional studies
Cross sectional -> case control -> cohort -> clinical
Increasing strength of proof of causality
What can cause incorrect associations between an exposure and a disease
Bias
Reverse causality
Confounding
Incorrect analysis
Chance
What is used to assess whether there is a causal relationship between an exposure and a disease
Bradford hill criteria
Aspects of Bradford hill criteria
Association strength
Dose response
Time sequence - exposure precedes outcome
Consistency of findings in other population
Biological plausibility
Coherence of evidence w other study types
Reversibility
