Question 2 It is known that there are a number of possible genetic risk factors

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Question 2

It is known that there are a number of possible genetic risk factors for Alzheimer’s disease. Certain alleles on the gene APOE are the most well known. Alzheimer’s is thought to effect 11% of poeople over the age of 65 in the United States. There are currently a large number of tests for Alzheimer’s. Consider a (fictitious) test that when administered to individuals over 65 years old:

Detects Alzheimer’s 94% of the time when it is present.

Detects Alzheimer’s 7% of the time when it is not present.

(a) What is the prevalence of Alzheimer’s in the population? (Those aged 65 years or more living in the United States.)

(b) What is the sensitivity of the test?

(c) What is the specificity of the test?

(d) What is the positive predictive value of the test?

(e) What is the negative predictive value of the test?

Explanation / Answer

(c)The specifity of the test is:

True negative/(true negative+false positive)

=(1-0.94)/(1-0.94+0.07)

=0.46

(d)The positive predictive value:

True positive/(true positive+false positive)

=0.94/(0.94+0.07)

=0.93

(e)The negative predictive value of the test:

True negative/(false negative+true negative)

=0.06/(0.93+0.06)

=0.06

(a)The sensitivity:

(true positive) / (true positive + false negative)

=0.94/(0.94+0.93)

=0.50

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