assessing the validity of screening and diagnostic tests

Question 1

what is the difference between sensitivity and specificity?

Answer 1

sensitivity = percentage of people with the disease who are correctly identified

specificity = percentage of people without the disease who are correctly identified

Question 2

what are positive and negative predictive values?

Answer 2

positive = percentage of all positive tests that are true positive tests

negative predictive value = percentage of all negative tests that are true negatives

Question 3

interpret this graph - determine the positive predictive value

Answer 3

only 234 of the 4443 positive tests were correct - therefore the positive predictive value is 5.3%

… therefore if you get a positive result, you’re 5.3% likely to have down syndrome