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24 Cards in this Set

  • Front
  • Back
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Classes of Mistakes
External Validity
Internal Validity
Execution
External Validity
Narrow research question not Clinically relevant. Inappropriate population or outcome
6 issues of Internal Validity
Fails to address narrow question.
Selection bias
Information bias
Misclassification
Confounding
Power
Surrogate Endpoint
Execution
missing data
inaccurate assays
data entry error
Synonyms: Exposure
Etiologic factor
Treatment, stimulus
Risk factor
Independent Variable
Prognostic Variable
Synonyms: Disease
health status
response variable
endpoint
dependent variable
outcome
Primary Study designs
Clinical Trial
Cohort
Case Control
Clinical Trial:
Risk
Risk Ratio
Risk Difference
Risk (E+): p1=a/N1
(E-): p0=b/N0
Risk Ratio: p1/p0
Risk Difference: p1-p0
Use vars from data layout
Strengths of RCT
Random
Strong Inferential Validity
Limits of RCT
Impractical:
rare disease
long follow-up
difficult to manipulate
Unethical
Impossible
Cohort:
Risk
Risk Ratio
Odds Ratio
Risk Difference
Risk (E+): p1=a/N1
(E-): p0=b/N0
Risk Ratio: p1/p0
Odds Ratio: (ad)/(bc)
Risk Difference: p1-p0
Use vars from cohort data layout
Cohort (variable follow-up)
Incidence Rate
Rate Ratio
Rate Difference
Incidence rate (E+) = I1 = a/T1
Incidence rate (E-) = I0= a/T0
Rate Ratio: IRR = I1/I0
Rate Difference: IRD = I1-I0
Strengths of Cohort Study
"Natural expriment"
Easy to understand
Limits of cohort study
Other differences betwen E+, E-

Impractical:
rare disease
long follow-up
Strengths of Case Control
Logistically Effecient
Good for rare disease
Efficient for sporadic exposures
Limits to case-control
More susceptible to bias
Difficult to understand
Unless nested: no disease rate
cannot always determine E after D
Inefficient for infrequent exposures
Differences between E+ and E-
Types of Ecological Studies
Geographic/Static exposure
Temporal or changing exposure
Limits to static ecologic studies
Temporal precedence
Variation in other factors
confounding
Ecological Fallacy
Ecological studies best when:
E is dominant risk factor for D
E is manipulated externally (change in policy) or other temporal variation
Secondary designs
partial cohort: E+ only
partial case-study: D+ only
Cross sectional
Why use E+ only
Very rare D and information needed quickly. Can be augmented with external controls.
Often use pre/post design
good and bad about D+ only?
limit of no D- group.
good if need info quick.
Limits of cross-sectional study
temporality:
E is altered by D+
Survival post D+ is affected by E
Inception Cohort
all individuals assembled at a given
point based on some factor, e.g. where they live or work