Problem 3.3. which is widely used as a screening test for Down\'s syndrome in ea

Question

Problem 3.3. which is widely used as a screening test for Down's syndrome in early pregnancy. The test measures the fluid under the skin at the back of the baby's neck and can be used to determine the risk of having a baby with Down's syndrome. The following table gives the test results for a sample of 1,000 pregnant women, with the age between 35 and 40: The nuchal translucency test is a special ultrasound scan Down Syndrome Baby Normal Baby Total Test+ Test - Total 50 945 995 53 947 1,000 Calculate: o the fale poalitive rate and fabe negative rate of the tent: (b) the sensitivity and specificity of the test; (c) the positive predictive value and negative predictive value of the test.

Explanation / Answer

Ans:

b)sensitivity=3/(3+2)=3/5=0.6

specificity=945/(50+945)=945/995=0.95

c)positive perdictive value=3/(3+50)=3/53=0.0567

negative perdicive value=945/(2+945)=945/947=0.9979

a)false positive rate=1-specificity=1-0.95=0.05

false negative rate=1-sensitivity=1-0.6=0.4

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