EBM Day 4 Flashcards
(51 cards)
Cohort Study vs Case Control
Cohort-know exposure, look how exposure level effects disease-start with cohort who are exposed (at risk for disease)
Case control-know disease, what factors give rise to disease-start with people with/without disease
Case control OR vs Cohort RR
Exposed CasesxNot exposed Noncases/not exposed cases x not exposed non cases
Exposed Cases x Exposed noncases/nonexposed cases x non exposed noncases
When OR is what, good idea of RR
Low-looking at disease that is not found much in population
Case control studies facts (that cohort can do)
- can’t yield incidence rates
2. can not give risk ratios
Case control strengths
- rare diseases
- diseases with long induction time
- explore wide range of exposures
- quick/cheap/easy/yields potential hypot
Bonferroni Correction
Correcting p values over multiple studies-leads to error
Random error, systematic error, bias
what do they look like
random error has points more spread out
bias moves points toward or further away from normal
systematic looks like a pattern
Oversampling
distorts odds ratio
Recall bias
Take unexposed or exposed and place in opposite group (because for recall)
Case definition traits
clear, specific, but not overly restrictive
misclassification if too broad
limited sample size if too strict
Should cases be incident?
Yes stop recall bias/less effect due to prolonged exposure
How to select controls
Should have same oppurtunity to have been exposed
-should be population risk at becoming a case
Should be sampled independent of exposure
- want people who are very similar except in exposure
-if not have selection bias
2x2 table
draw
Diagnostic/Workup Bias
Case selection influenced by physicians knowledge of exposure
Nested Case Control Studies
Select cases and controls from cohort study
More eficient- already have most info
healthy worker effect
People who work are more healthy then those who do not
Matching
control selection coupled with experimental selection to reduce confounding variables
More controls
Increase power until 4, then not worth
Non differential misclassification vs differential misclassification and what error they lead to
Exposure unrelated to disease (chance)
All different groups (variables) have equal rate of being misclassified
Leads to type II error
Different groups have unequal rate of being misclassified
Leads to type 1 or t2 error
Information bias
bias due to measurement error
How to minimize recall bias
Using records of exposure to disease, use incident cases, appropriate control, blind study, etc.
Investigator bias and how to not have
Investigator does something like leading questions because knows exposure status he is looking for
Standerdized protocols, objective measurements, blinding
Adv of case control studies
rare disesase, new disease, outbreaks, induction period is long, inexpensive, multiple expusres
Disadv of case control studies
Bias (recall and misclassifcation), singe out come, inefficient if low freq, does not calculate incidence rate directly
