1.1 Suppose a certain drug test is 99% sensitive and 99% specific. The test will correctly identify a drug user as testing positive 99% of the time, and will correctly identify a non- user as testing negative 99% of the time. This would seem to be a relatively accurate test, but Bayes' theorem can be used to demonstrate the relatively high probability of misclassifying non-users as users. Assuming a corporation decides to test its employees for drug use, and that only 0.5% of the employees actually uses the drug. What is the probability that, given a positive drug test, an employee is actually a drug user? (8 marks)
