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| Block 1: Epidemiology |
| EPI3-2: ABSOLUTE MEASURES OF COMPARISON OF DISEASE OCCURRENCE OR MEASURES OF EFFECT |
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| Block 1: Epidemiology |
| EPI3-2: ABSOLUTE MEASURES OF COMPARISON OF DISEASE OCCURRENCE OR MEASURES OF EFFECT |
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SESSION OBJECTIVE |
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At the end of this session you should be able to calculate three absolute measures of effect from 3 measures of occurrence and data provided for the latter. |
For all the 3 measures of occurrence, there are 3 corresponding absolute measures of effect:
If the incidence proportion of lung cancer during a 15 year period is 0.0010 for smokers and 0.0001 for non-smokers, the absolute difference in incidence proportion or incidence proportion difference would be 0.0009.
| Findings from a hypothetical prevalence study of 20 000 persons at the point in time when the cohort study which will follow up 20 000 persons without the disease for 10 years begins | |||
|---|---|---|---|
| Exposed | Non-exposed | Ratio | |
| Prevalent cases | 200 | 100 | |
| Non-cases | 10 000 | 1 000 | |
| Prevalence | 0.02 | 0.01 | 2.0 |
| Findings from a hypothetical cohort study of 20 000 persons followed for 10 years | |||
| Cases Non-cases |
1 813 (a) 8 187 (c) |
952 (b) 9 048 (d) |
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| Initial population size | 10 000 (N1) | 10 000 (N0) | |
| Person-years | 90 635 (Y1) | 95 163 (Y0) | |
| Incidence rate Incidence proportion (average risk) Incidence odds |
0.0200 (I1) 0.1813 (R1) 0.2214 (O1) |
0.0100 (I0) 0.0952 (R0) 0.0152 (O0) |
2.00 1.90 2.11 |
Another example from the table above shows the incidence proportion difference to be 0.1813 - 0.0952 = 0.0862
