psychiatric researcher wishes to evaluate a new diagnostic instrument for psychotic illness.

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A psychiatric researcher wishes to evaluate a new diagnostic instrument for psychotic illness. The test is comprised of 20 questions regarding individual psychiatric symptoms.A positive test is one in ‘with a score of at least 16 of the 20 symptoms. The sensitivity of the test was determined to be 0.96, while the specificity is 0.99. The following gives the psychotic disease prevalence rates for two subpopulations of people:

Subpopulation Prevalence

General Population 0.001

Homeless 0.1

a. Compute predictive values of a positive and negative test for each of the above

subpopulations.

b. Suppose that predictive vaLue of a positive test of greater than 0.5 is deamed

acceptable. Under this criterion, what subpopulations should recieve the test.

c. Suppose that we have a sample of 1000 homeless with positive test results.

i.How many of those people do you expect to actually have psychotic illness?

ii. How many of those people do you expect not to have psychotic illness?

 

Take a look at the following article on diagnostic testing:

Gibot. S.. et al, (2004). Soluble thggenng receptor expressed on niyeloid cells and the diagnosis of pneumonia. New England Journal of Medicine 150. 451-458.

a. What disease are the authors attempting to diagnose? Be specific.

b. What bloinarkers are being considered for the disease?

c. Figure 2 gives the ROC for the three biomarkers.

i. Give the areas under the curve for the three biomarkers. (Hint: look at the figure legend).

ii. Based on the ROC curves, which bioniarker performed best? Which performed the worst?

« Which biomarker was selected by the authors? Was this the best performing biomarker? (Hint: see text pp. 455-456)

e. What screening value was selected for the selected biomarker?

f What is the sensitivity and specificity of the biomarker under the selected screemng value?

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