Your study enrolls 10,000 adults age 218 years old between 2004-2005 who present
ID: 3329290 • Letter: Y
Question
Your study enrolls 10,000 adults age 218 years old between 2004-2005 who present at one of the Department of Motor Vehicles office throughout NJ for license renewal, first time licenses, registration services, etc. You conduct follow-up on these individuals for 5 years after enrollment. Information on cause of death is ascertained by reviewing death certificates, records from the Medical Examiner's office, etc. At the end of the study, you have accumulated the following data n=180 total motor vehicle related deaths; among these 180 deaths, n=100 were due to driving in excess of the speed limit, n=45 deaths due to driving while intoxicated and n 35 deaths due to other, unidentified reasons (important note: all of these causes of death are mutually exclus You are able to construct the following two 2x2 tables with your cohort study data: Table 1: Deaths related to driving speed: Died Not dead Driving in excess of the 100 1900 2,000 speed limit Driving within speed 80 180 7920 9820 8,000 10,000 limit Table 2: Deaths related to driving while intoxicated (DWI) Died 45 135 180 Not dead 255 9565 9820 300 9,700 10,000 DWI No DWIExplanation / Answer
a.
Cumulative Incidence among the Drive in excess of speed limit = 100 / 2000 = 0.05
Cumulative Incidence among the Drive within speed limit = 80 / 8000 = 0.01
Risk Difference = 0.05 - 0.01 = 0.04
b.
Cumulative Incidence among DWI = 45 / 300 = 0.15
Cumulative Incidence among No DWI = 135 / 9700 = 0.014
Risk Difference = 0.15 - 0.014 = 0.136
c.
The excees risk of death when Drive in excess of speed limit is 0.04.
The excees risk of death when driving intoxicated in excess of speed limit is 0.136
a.
Proportion of mortality due to driving speed = 100 / 2000 = 0.05
b.
Proportion of mortality due to DWI = 45 / 300 = 0.15
c.
The percentage of mortality in the exposed group due to driving speed is 5%
The percentage of mortality in the exposed group due to DWI is 15%
a.
Outcome rate exposed (Pe) = 100/2000 = 0.05
Outcome rate not exposed (Pu) = 80 / 8000 = 0.01
Relative risk (RR) = 0.05 / 0.01 = 5
Estimate of population exposure (Px) = 2000 / 10000 = 0.2
Population attributable risk % = 100*(Px*(RR-1))/(1+(Px*(RR-1)))
= 100*(0.2*(5-1))/(1+(0.2*(5-1))) = 44.44%
b.
Outcome rate exposed (Pe) = 45/300 = 0.15
Outcome rate not exposed (Pu) = 135 / 9700 = 0.014
Relative risk (RR) = 0.15 / 0.014 = 10.71
Estimate of population exposure (Px) = 300 / 10000 = 0.03
Population attributable risk % = 100*(Px*(RR-1))/(1+(Px*(RR-1)))
= 100*(0.03*(10.71-1))/(1+(0.03*(10.71-1))) = 22.56%
c.
The percentage of mortality in the study population that is attributable to the driving speed is 44.44%
The percentage of mortality in the study population that is attributable to DWI is 22.56%
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