Compute the PV− under these altered assumptions. How does the true PV− using a screening criterion of SCN ≥ 100 μg/mL for identifying smokers compare with the PV− based on self-reports obtained in Problem 3.73? 

Suppose we regard the self-reports of all students who report some cigarette consumption as valid but estimate that 20% of students who report no cigarette consumption actually smoke 1–4 cigarettes per week and an additional 10% smoke 5–14 cigarettes per week.