suppose that 79% of hypertensives and 25% of normatensives are classified as hypertensive by an automated bloo

Question

ok here is the question from the begining:
suppose that 79% of hypertensives and 25% of normatensives are classified as hypertensive by an automated blood-pressure machine.Assuming that 18% of the population is hypertensive, find:
(a) the predictive value positive of the blood-pressure machine. interpret your answer. (b) the predictive value negative of the blood-pressure machine.interpret your answer NOTE: please use the notation (T,D, etc)

Answer 1

The machine misses 21% of the hypertensives.

Answer 2

positive predictive value:

# true positives / (# true pos. + # false pos.)

Use percentages for these:
# true positives = 0.18
# false positives = 0.25 * 0.82 (because 82% of the population is normatensive, and 25% of them are classified as hypertensive)

Negative predictive value:

# true negatives / (# true neg. + # false neg)

# true neg = 0.82
# false neg = 0.18 * 0.21 (because 21% of hypertensives are not classified as hypertensive, and 18% are hypertensives)

Intuitively, a high positive predictive value (near 1) means it's useful for identifying if someone is hypertensive, whereas a high negative predictive value means it's useful for detecting if someone isn't.

Sorry, that's all I can help you with.