### sequential usmle biostats question

Posted:

**Wed Apr 20, 2016 3:52 am**An imaginary study involving 650 people was conducted to assess the performance of the stool antigen assay in detecting a helicobacter pylori infection. After collecting all the test results, it was found that 250 people tested positive and 400 people tested negative. If the positive and negative predictive value were 80% and 75%, respectively, then what proportion of people with the infection were identified by the test?

(A) 300/650

(B) 200/250

(C) 200/300

(D) 200/650

How would the sensitivity of the test change if the number of positive tests was higher?

(A) It would increase

(B) It depends on the prevalence

(C) Not enough information is provided

(D) It would decrease

What would the sensitivity of the test be if 10 people with the condition did not test negative?

(A) 200/310

(B) 210/300

(C) 210/310

(D) 200/300

The answers and explanations can be found on youtube via this link... https://www.youtube.com/watch?v=2fe_kjH_bbk

(A) 300/650

(B) 200/250

(C) 200/300

(D) 200/650

How would the sensitivity of the test change if the number of positive tests was higher?

(A) It would increase

(B) It depends on the prevalence

(C) Not enough information is provided

(D) It would decrease

What would the sensitivity of the test be if 10 people with the condition did not test negative?

(A) 200/310

(B) 210/300

(C) 210/310

(D) 200/300

The answers and explanations can be found on youtube via this link... https://www.youtube.com/watch?v=2fe_kjH_bbk