<prompt> An experimental diagnostic test is developed to noninvasively detect the presence of trisomy 21, Downs syndrome. The test is administered to a group of 500 women considered to be at risk for a Downs fetus based on blood tests. The results of this test are shown below. What is the sensitivity of this new test? rn rnrnrn rnrnTrisomy 21rnrnrnNormal KaryotypernrnrnrnrnPositive Testrnrnrn100rnrnrn50rnrnrnrnrnNegative Testrnrnrn100rnrnrn250rnrnrnrn40506771  <response>: Sensitivity is defined as the ability of a test to detect the presence of a disease in those who truly have the disease. It is calculated as the number of people with a disease who test positive true positive divided by the total number of people who have the disease true positive false negative. In this case, sensitivity equals the number of babies born with trisomy 21 whose mothers tested positive 100 divided by the total number of babies born with trisomy 21. This yields 100200 50 not a very sensitive test. 40 corresponds to the prevalence of the disease in the tested population, which in this case equals the total number of babies with Downs syndrome true positive false negative 100 100 200 divided by the total number of people tested 500. This yields 200500 40. 67 corresponds to the positive predictive value of the test, which equals the number of babies with Downs whose mothers test positive true positives 100 divided by the total number of mothers testing positivetrue positive false positive 150. This yields 100150 67. 71 corresponds to the negative predictive value of the test, which equals the number of normal babies whose mothers tested negative 250 divided by the total number of people testing negative 350. This yields 250350 71. 