1. A test with 99% sensitivity and 95% specificity is applied to three populatio
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Question
1. A test with 99% sensitivity and 95% specificity is applied to three populations. Population A has a prevalence of 1%. Population B has a prevalence of 10%. Population C has a prevalence of 20%. Each population has exactly 1000 people.
Please complete the following table:
Population
A
B
C
Number in Population
1000
1000
1000
Prevalence
1%
10%
20%
Number Diseased
Number Not Diseased
Number of True Positives
Number of False Positives
Total number positive on the test
Positive Predictive Value
Population
A
B
C
Number in Population
1000
1000
1000
Prevalence
1%
10%
20%
Number Diseased
Number Not Diseased
Number of True Positives
Number of False Positives
Total number positive on the test
Positive Predictive Value
Explanation / Answer
Population
A
B
C
Number in Population
1000
1000
1000
Prevalence
1%
10%
20%
Number Diseased
10
100
200
Number Not Diseased
990
900
800
Number of True Positives
0.99x10 = 9.9 = 10
0.99x100 = 99
0.99x200 = 198
Number of False Positives
0.05x990 = 50
0.05x900 = 45
0.05x800 = 40
Total number positive on the test
60
144
238
Positive Predictive Value
(10/60)x100 = 16.67%
(95/144)x100 = 65.97%
(198/238)x100 = 83.19%
Population
A
B
C
Number in Population
1000
1000
1000
Prevalence
1%
10%
20%
Number Diseased
10
100
200
Number Not Diseased
990
900
800
Number of True Positives
0.99x10 = 9.9 = 10
0.99x100 = 99
0.99x200 = 198
Number of False Positives
0.05x990 = 50
0.05x900 = 45
0.05x800 = 40
Total number positive on the test
60
144
238
Positive Predictive Value
(10/60)x100 = 16.67%
(95/144)x100 = 65.97%
(198/238)x100 = 83.19%
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