Epidemic CurvesSensitivity/Specificity

Epidemic Curve

Time (since exposure)

Num

ber

of N

ew

Cas

es

Notes on Epidemic Curves

• Sort by time to illness

• Think critically about the data (possible problems)

• Ask questions (or make assumptions)

• Similar to Survival Curve (see text, p492)

Survival from AIDS in Mths (p492 in text)

Pt # Surv. Mths

1 2 0.9167

2 3 0.9091

3 6

4 6 0.800

5 7 0.857

6 10

7 15 etc

8 15

9 16

10 27

11 30

12 32

n tq1

0.083312

1

0.090911

Hazard

20.2

10

10.125

8

See Table 21.3 in Text (page 493)

1 n tqSurvival Rate

Sensitivity/Specificity (p136 in text)

• Used in Screening or diagnostic Tests when there is a ‘gold standard’

• Sensitivity: pr(+| ill)

• Specificity: pr(-| not ill)

• Suppose eating a food item is a ‘test’. If yes, the person should be ill. If no, not ill.

• Use ‘symptoms’ as the ‘gold standard’