差分

**a)

***Positive predictive value=<math>\frac{38}{38+1999.2}=0.187</math>***Negative predictive value=<math>\frac{97960.8}{2+97960.8}=0.999</math>

**b)

***Positive predictive value=<math>\frac{316.35}{316.35+13.34}=0.959</math>***Negative predictive value=<math>\frac{653.66}{1999.2+653.66}=0.246</math> *Q4To have high sensitivity is more important, because testing blood donor is a screening test and false-negative has to be excluded as much as possible. *Q5We need to calculate PPV and show the director how much false-positive donors arise in order to advise not to inform test-positive donors without additional confirmation tests.