Attributable Risk A hypothetical cohort study looked at the association between
ID: 3272555 • Letter: A
Question
Attributable Risk
A hypothetical cohort study looked at the association between family history and the risk of developing Alzheimer’s disease. The results were as follows:
Alzheimer’s Disease
No Alzheimer’s Disease
Totals
Incidence of AD
Family History
50
1,950
2,000
25 per 1,000
No Family History
25
2,975
3,000
8.3 per 1,000
3. Now assume the prevalence of family history in the general population is 25%. What effect does this change have on the estimate of the population attributable risk? Discuss the relationship between the population prevalence of exposure and the population attributable risk. Why is it important to understand this relationship as a public health professional? (must show work)
Alzheimer’s Disease
No Alzheimer’s Disease
Totals
Incidence of AD
Family History
50
1,950
2,000
25 per 1,000
No Family History
25
2,975
3,000
8.3 per 1,000
Explanation / Answer
p = Prevalance of family history in general population = 0.25
Population attributable risk = Proportion of cases that can be attributaed to the risk of exposure to a disease
= cases of exposure due to disease / total population
= p*(RR-1)/ (1+ p*(RR-1)), where RR is the relative risk of the effect of the disease
So, this depends on p and a change in p leads to change in PAR
The relationship between PAR and PPE is as follows:
PAR=PPE*AR
where AR = Attribute Risk = (Number of people exposed - number of people unexposed)/ Number of people exposed
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