1. Lessons from Epi Midterm (S05)
Reflections +

2. Validity is the Goal
Axiom: There is no such thing as a perfect test (Chap 4)
Corollary 1: All test results require interpretation
Corollary 2: A test does not have to be perfect to be useful

3. Why name appears outside only
Blinding increases likelihood grade will not be based on prior belief  increasing validity
Blinding does not remove random error

4. Q1
Why was kappa was given?
Goal is interpretation (not arithmetic)

5. Q2 Q2 Lay people may refer to all these as “rates”
Prevalence
Incidence proportion (risk)
Incidence rate
Lay people may refer to all these as “rates”
But we know better
Rate  risk when disease is rare
Prevalence  Incidence × Duration

6. Q3
Group project has some benefits
But leaves some individuals behind

7. Q4
Vital statistics in an open population
No problems in calculations

8. Question 5 “By How Much?” Which population has a higher rate?
And “By how much?”
Introduces the concepts in Chapter 8
Answer on exam showed good intuition

9. Ways to quantify differences
Relative difference
Absolute difference
“Impact” of exposure

10. Relative Difference Relative difference derived by ratios Suppose
e.g., “Twice the rate”
Suppose
Group 1 rate is 200 per 100,000
Group 0 rate is 100 per 100,000
Let RR represent the relative risk

11. Absolute Difference Absolute difference derived by subtraction
Let RD represent the risk difference

12. Potential Impact There are two ways to discuss “impact”
Let’s consider the effect of the exposure in exposed cases
Assume difference in risk entirely due to exposure
Population 1 risk would revert to the population 0 risk if exposure was averted
This is the Attributable Fraction in the exposed (AFe)
Illustrative example: