Evidence based practice Diagnosis (2)


1. Under which of the following situations is the person tested very UNLIKELY to have the disease?

One answer only.
   A test with a high sensitivity is positive.
   A test with a high sensitivity is negative.
   A test with a low sensitivity is positive.
   A test with a low sensitivity is negative.
   A test with a high specificity is positive.
   A test with a low specificity is negative.


2. Under which of the following situations is the person tested very LIKELY to have the disease?

One answer only.
   A test with a high sensitivity is positive.
   A test with a high sensitivity is negative.
   A test with a low sensitivity is positive.
   A test with a low sensitivity is negative.
   A test with a high specificity is positive.
   A test with a low specificity is negative.


3. In a population, one-fifth of the population suffers from a disease. The odds of a person in the population having the disease is

One answer only.
   1/5
   1/4
   1/3
   4/5
   3/4


4. Continuing on from question 3, the probability of a person NOT having the disease is

One answer only.
   1/5
   1/4
   1/3
   4 /5
   3/4


5. This scenario applies to questions 5 to 8. One hundred (100) patients admitted to the coronary care unit suspecting of having a myocardial infarct (heart attack) received both conventional diagnostic tests (clinical history, serial ECGs, serial cardiac enzymes) and a new screening test T of unknown usefulness. Out of seventy (70) patients were found to have myocardial infarct by conventional diagnostic tests, 14 were found to be negative for test T. Out of those who did not have a myocardial infarct, six patients were tested positive by test T. The sensitivity of the test is:

One answer only.
   50%
   60%
   70%
   80%
   90%


6. The specificity of the test is

One answer only.
   50%
   60%
   70%
   80%
   90%


7. How many times more likely is a patient with a myocardial infarct to be tested positive than a patient without the myocardial infarct?

One answer only.
   2.5 times
   3 times
   3.5 times
   4 times
   4.5 times
   5 times
   None of the above


8. What is the measure in question 7 above called?

One answer only.
   Sensitivity
   Specificity
   Positive predictive value
   Negative predictive value
   Likelihood ratio for a positive test
   Likelihood ratio for a negative test


9. You decide to use this test T described in questions 3 – 8 above for your patients Emergency Department presenting with chest pain. From previous audit, you know that, on average, about 20% of such patients prove to have a myocardial infarct. One of your patient in Emergency Department was tested positive. What is his pre-test odds for having a myocardial infarct?

One answer only.
   1/6
   1/5
   1/4
   1/3
   1/2


10. From your answers to questions 8 and 9, what is the post-test odds of this patient having a myocardial infarct?

One answer only.
   1/4
   1/3
   1/2
   1
   2
   3
   4


11. So, what is the probability that this patient who was tested positive had a myocardial infarct?

One answer only.
   25%
   33%
   50%
   70%
   75%
   100%