Scenario 1: The prevalence (a + c in the table below) of previously undetected diabetes in a population to be screened is approximately 1.5% and it is assumed that 10,000 persons will be screened.The screening test will measure blood serum sugar content.A value of 180 mg/dl or higher is considered positive.The sensitivity (a) and the specificity (d) associated with this screening are 32.9% and 99.8% respectively. (1 point per box)

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Sensitivity (ill) =

a/(a+c) x 100 = 32.9%

Specificity (well) =

d/(d+b) x 100 = 99.8%

Total

people

Disease Present

Disease Absent

Positive tests

(A)True +

A=49.35

(B) False + , Type 1

B=19.7

(A+B) positive tests

A+B=69.05

Negative tests

(C)False -, Type II

C=100.65

(D) True -D=9830.3

(C+D) negative tests

C+D=9930.5,

\.,,T,otal tests

(A+C) Prevalence of Ills = 1.5%

A+C=150

(B+D) Wells =

B+D=9850

10,000

Population

Use Scenario 1 data to calculate your answers to questions 22-26 (10 points)

Points

9.The percentage of false positives among all those without the condition (the Type I Error Rate, or 1 - specificity), or b/(b+d)

1 - specificity = ____%,

or b / (b + d)

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10.The percentage of false negatives among all those with the condition (the Type II Error Rate, or 1 - sensitivity), or c/(a +c)

1 - sensitivity = ____%, or c / (a + c)

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11.The predictive value of a positive (PPV) test,

or = a / (a + b)

PPV= ____ %

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12.The predictive value of a negative (NPV) test,

or = d /(d + c)

NPV= ___%

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13.Based on the calculations above, how many false positives and negatives will occur if 100,000 people are screened? (100,000 / 10,000 = 10)

false positives= __/ 100,000 cases

false negatives= __/ 100,000 cases

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