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-,At risk New cases Age (yrs)Notes:11. All numbers except incidence rate are roundedafter ( ) years
Instructions:d1. To see the effect of the incidence rate (a.k.a. "incidence density") on the incidence proportion(10-year IP) Incidence(average IR) rate (IR)proportion (IP)Accumulatedcasesb2. The number of 30-year-olds at risk was chosen so that the total number of people 30-39 at riskOverallb at risk, equivalent to dividing the average number of cases per year by the average number of! people at risk in each year.vjs@unc.edu^4. The above tables shows what would happen to a cohort of 30-year-olds during the years they_ become 31, 32, 33, & , 39. It can also be viewed as what happens in 1 year in a population_ of 10,005 30-39-year-olds. The difference depends upon whether you regard the variable ina column B (age) as the current age of the 10,005 in the population or the attained age of the2 1,023 people who started at age 30 in year 1.per yearQ (a.k.a. "cumulative incidence"), change the assumed incidence rate (in blue).\3. You can examine the formulas to see how numbers are calculated by clicking on a cell and+ looking in the formula bar at the top.P For example, try replacing 0.005 with 0.05 or, for a dramatic effect, 0.20.Z would be about 10,000 if the incidence is 5/1,000 per year; you can change that cell.c3. The average IR was obtained by dividing the total number of cases by the total number of people (rounded)dExample of incidence rate and incidence proportion for first occurrence of major depressive disorder^(MDD) in adults 30-39 years old during a 10 year period (Vic Schoenbach, 9/6/2002, 1/25/2004).72This table shows what would happen in a cohort of #30-year-olds at risk of MDD as theyKage through their thirties, assuming that the incidence rate is constant atc2. All other cells except the number in the cohort contain formulas or constants, so do not change them inadvertantly.b4. The two graphs show the incidence proportion and the decreasing size of the population at risk[ over the 10 years. Examine the charts before and after you modify the incidence rate.J(See IncidenceRateIncidenceProportion.doc for explanation of the example.)>Victor J. Schoenbach, www.epidemiolog.net, 9/6/2002, 1/25/20042
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