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14 Cards in this Set
- Front
- Back
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Definition of groups
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Appropriate definition, classification and measurment of expsure. Analogous to randomization in CT
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Examples of exposure groups
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Genetics
Age Demographics Lifestyle Geographoc Environmental Disease Meds Devices Education Policies |
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6 - Exposure checklist
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1) External E-
2) Internal E- 3) Zero time 4) Classification 5) Measurement 6) Change w\ follow-up |
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Internal E-
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cohort is single group of subjects with uniform procedures.
Classification (E+ or E-) done at same time (t0). Can be matched or entire E- |
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Increasing comparability of E- group
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try and restrict E- to subjects most similar to E+ (some covariate that makes them very similar to E+)
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Using alternative exposure for E-
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careful of counfounding. Can show erranous protective effect. Should try and use plocebo or no exposure.
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Temporal E- comparisons: Natural crossover
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uses person time of exposure compared to person time of unexposed.
t0 should be at initial intervention..not follow/up |
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External E-
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Group from a different population.
Different procedures to identify and collect data. |
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3 Fundamental weakness of E-
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1)Effect of different procedures cannot be separated from the effect of E.
2)Entire group risk of D may be different (healthy worker effect) 3)Usually E+ data more complete |
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External E - Comparison at Different institutions
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Must take care that patients are treated exactly the same.
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External E: Control group membership influenced by D
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E- Should have same chance of getting exposure an getting outcome as E+
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Zero time
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inception cohort - patients should be identified at an early and unambiguous point in the course of their disease. It is a challege for E-
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Reference category
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reference group with which others are compares in calculating measured effect (often lowest quintile of exposure).
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3 ways to Constructing Categories
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1)Intrinsically meaningful divisions
2)Percentiles (if no a priori H) 3)Don't torture the data |
