Chapter 10 (from in class packet) Flashcards
What are the 2 measures of association?
risk and odds
what are the 4 steps to case-control studies?
- select 2 groups of people with disease and without disease
- ascertain the exposure
- determine the PROPORTION of EXPOSED among the cases and the PROPORTION OF NONEXPOSED among the cases. the same with controls
- the proportion of cases who were exposed is compared with the proportion of controls who were exposed
what is the formula for risks (measures of association)
chances of something happening/ chances of ALL things happening
what is the formula for odds (measures of association)?
chances of something happening/ chances of NOT happening
what is the probability that the event does not occur? (equation)
1-p
what is the odds of the event equation?
O= p/1-p
what is the odds ratio?
the odds of exposure among the cases/the odds of exposure among the controls
what is the MEASURE of ASSOCIATION between disease and exposure in a case-control study?
OR= ad/bc
what is the odd EXPOSURE in the cases is EQUAL to the odds of exposure in the controls (no association)
OR=1
what is the odds of EXPOSURE in the cases is GREATER than the odds of exposure in the controls (positive association)?
OR>1
what is the odds of EXPOSURE in the cases in LESS than the odds of exposure in the controls (negative association)? protective effect
OR<1
when the disease IS RARE what happens?
OR~RR
When the disease is NOT RARE what happens?
OR>RR
what is the process of selecting the controls so that they are similar to the cases?
matching
if you match too many characteristics then what happens?
it will be difficult to identify an appropriate control
if you match on a given characteristic can you use this characteristic again?
NO
which OR do you use during a matched case-control study?
b/c
What are the 4 steps when doing a CASE selection?
- establish a case definition
- cases can be new cases or existing case
- cases must be representative of persons with disease
- sources: hospitals, ph clinics, physician offices, HMOs, diseases registries
What are the 4 steps when doing a CONTROL selection?
- controls are subjects free of disease
- controls should come from the same source of population as the case
- the prevalence of exposure of the controls should be similar with the prevalence of exposure among the source of population
- sources: general population, random digit dialing, friends/relatives, hospital or clinic based
how many controls per case?
1:1
How can the number of case be increased?
by using more than one control case
what are the 2 parts of assess exposure?
- study subjects
- existing records
what are study subjects?
self-reported questionnaire
- particularly vulnerable to recall bias as cases may recall their exposure history more thoroughly than controls
What is existing records?
- work histories (industrial hygiene)
- hospital (birth, diagnostic, x-ray)
- prescriptions
List case-control study advantages.
- quick and expensive
- small sample sizes
- optimal for evaluation of rare diseases
- can examine multiple etiologic factors for a single disease
List case-control study disadvantages
- inefficient evaluation of rare exposures unless the disease is common among the exposed
- disease status can influence the selection of case and control subjects
- may be difficult to establish the temporal relationship between exposure and disease. exposure measurements are collected after disease occurence
- prone to bias compared to analytic designs, in particular, selection and recall bias
When does nested case-control study occur?
- after the establishment of a cohort study
List some advantages of a nested case-control study
- decrease in recall bias
- identify risk factors, rather than early or subclinical disease as the specimens were obtained years before disease occurs
- less expensive
- increased comparability
