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Epidemic Curves SensitivitySpecificity

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Epidemic Curves SensitivitySpecificity Powered By Docstoc
					 Epidemic Curves
Sensitivity/Specificity
                      Epidemic Curve
Number of New Cases




                          Time (since exposure)
    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) Hazard q Survival
                         1    Rate
    Pt #       Surv. Mths          n   qt          n    t
                                 1
    1          2                     0.0833   0.9167
                               12
                                1
    2          3                    0.0909    0.9091
                               11
    3          6
                                2
    4          6                   0.2        0.800
                               10
                               1
    5          7                  0.125       0.857
                               8
    6          10
    7          15            etc
    8          15
    9          16
    10         27
    11         30
    12         32

           See Table 21.3 in Text (page 493)
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’

				
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posted:1/31/2013
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