A diagnostic test for a disease is known to have a sensibility (i.e. the probability that the test is positive if the individual is infected) of 90% and specificity (i.e. the probability that the test comes up negative if the individual is healthy) of 70%. Half the tests in a massive screening yield positive results.
1. (3) Which is the frequency of the disease in the population?
2. (2) Which is the probability that an individual is infected if the test is positive