Negative Predictive ValueFind the negative predictive value for the test. That is, find the probability that a subject does not use drugs, given that the test yields a negative result.

Identical and Fraternal Twins.use the data in the following table. Instead of summarizing observed results, the entries reflect the actual probabilities based on births of twins (based on data from the Northern California Twin Registry and the article “Bayesians, Frequentists, and Scientists” by Bradley Efron,Journal of the American Statistical Association,Vol. 100, No. 469). Identical twins come from a single egg thatsplits into two embryos, and fraternal twins are from separate fertilized eggs. The table entries reflect the principle that among sets of twins, 1/3 are identical and 2/3 are fraternal. Also, identical twins must be of the same sex and the sexes are equally likely (approximately), and sexes of fraternal twins are equally likely.

Fraternal Twins

a.After having a sonogram, a pregnant woman learns that she will have twins. What is the probability that she will have fraternal twins?

b.After studying the sonogram more closely, the physician tells the pregnant woman that she will give birth to twins consisting of one boy and one girl. What is the probability that she will have fraternal twins?

Solution 26BSC

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