Question

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 22.9% and 99.8% respectively.

Questions 1-9: set up a two by two table with the appropriate numbers in each cell of the table. Round to the nearest whole number, but only after you have completed all the calculations down through. (Condition Absent or Present is determined by symptoms.) (1 point per box)

/9 points	Ills	Wells	Total people
Positive tests	(A or True +) 34.35	(B or False +) 19.7	(A+B or all positive tests) 54.05
Negative tests	(C or False - ) 115.65	(D or True -) 9830.3	(C+D or all negative tests) 9945.95
Total tests	(A+C or all ills) 150	(B+D or all wells) 9850	10,000 Total Population

Calculate as indicated	Answer (2 pts. each)	Points
The percentage of false positives among all those without the condition (the Type I Error Rate, or 1 – specificity), or b / (b + d)		/2
The percentage of false negatives among all those with the condition (the Type II Error Rate, or 1 – sensitivity), or c / (a + c)		/2
The predictive value of a positive (PPV) test, or = a / (a + b)		/2
The predictive value of a negative (NPV) test, or = d / (c + d)		/2
Based on the calculations above, how many false positives and negatives will occur if 100,000 people are screened?		/2

Answer 1