Incidence
| = (number of people developing an outcome ÷ the number in a population) during time T |
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Exposure group occurrence [EGO] or experimental event rate [EER]
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| = a ÷ E during time T = a ÷ (a+c) during time T = (a ÷ (a+c))/T |
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Example: Incidence of CHD death in HRT group from HERS3 |
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| EGO (or EER) |
| = [71 events ÷ 1380 women] over 4.1 years = 51.5 events per 1000 women over 4.1 years = 12.5 events per 1000 women per year |
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Comparison group occurrence [CGO] or control event rate [CER]
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| = b ÷ C during time T = b ÷ (b+d) during time T = (b ÷ (b+d))/T |
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Example: Incidence of CHD death in placebo group from HERS3 |
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| CGO (or CER) |
| = [58 events ÷ 1383 women] over 4.1 years = 41.9 events per 1000 women over 4.1 years = 10.2 events per 1000 women per year |