case control studies

Question 1

case control study

Answer 1

cases are compared to controls
with respect to exposures of interest
if exposure higher in cases - risk factor
lower - protective
retrospective - exposure difficult unless it is persistant egf genetics/there are records

Question 2

use of case control

Answer 2

identify potential causes of the disease
explore association between risk factors
identify clinical patterns, presentations and associations

Question 3

selection of cases

Answer 3

inbclusion criteria and recruitment framework
state whertehr prevalent or incident cases
how cases will be identified
should be representative of whole population - unless stated otherwise - ie just looking at one part of the spectrum

Question 4

selection of controls

Answer 4

representative of cases and come from the same population
randomly selected from the population, may have other conditions, matched to case - friend or neighbour
may be >1 control per case- increase the power to exclude chance as an observation - good when cases are rare

Question 5

measurement of exposure

Answer 5

questionnaire
past records
same method in cases and controls

Question 6

analysis

Answer 6

prevalence of exposure in case and control
odds ratio
matched cases and controls - complex analysis using conditional logistical regression models

Question 7

odds ratio

Answer 7

odds exposure in case/odds exposure in control

Question 8

odds ==

Answer 8

prevalence/(1-prevalence)

Question 9

strength

Answer 9

quick and cheap -if long latent periods between exposure and condition
efficient for rare disease
several risk factors for 1 disease

Question 10

limitation

Answer 10

cant measure incidence
recall and selection bias
inefficient for rae exposures
temporal unsure