Observational studies Flashcards
What are some kinds of observational study?
Case controlled
Cohort
Why do observational studies?
To generate a hypothesis
Cheaper than RCT
Can study rare events
Easier ethically
What is a case controlled study?
Where you compare those with a condition to those without and looks at exposure to risk factors
What are the odds of exposure?
The chances that someone with a condition has been exposed to a risk factor:
Diseased exposed/diseased non-exposed
Non-diseased exposed/non-diseased non-exposed
What are odds ratios?
Odds of diseased/odds of non-diseased
What kinds of bias can occur in case controlled studies?
Selection bias
Observer bias
Recall bias
Survivor bias
What is selection bias?
Group picked may not represent population
What is observer bias?
Knowledge of who has what may affect data gathering, ie. ID higher risk stuff in diseased
What is recall bias?
Recall possibly unlinked events and blame them or better recall in diseased group as thought about more
What is survivor bias?
Where many people die before become counted as a case.
What is a confounding variable?
A variable that is independently associated with exposure and disease
What is a cohort study?
Follow a population and see who is exposed to risk factors and who is not and who develops disease and who doesn’t
What are cohort studies good for?
Rare events- radiation exposure etc
MUltiple outcomes related to infrequent exposure
Disease incidence
How risk changes over time
How do you calculate the incidence risk in cohort studies?
Diseased exposed to risk factor/total exposed to risk
How do you calculate the relative risk in a cohort study?
Incident risk in exposed / risk of disease in unexposed
