








USMLE Step 1 Forum USMLE Step 1 Discussion Forum: Let's talk about anything related to USMLE Step 1 exam 

Thread Tools  Search this Thread  Display Modes 
#1




Another Statistics question solve this
B thalassemia major results from a homozygous genotype that leads to comple of both the bglobin chains, A study subjected 100,000 participants to an intrauterine screeting test; 87 tested positive for B thal major, and the remaining 99,913 tested negative. In 7 of those 87 cases the results were shown to be false positive, Ultimately 100 of those originally screened were found to actually have the disease, which of the following is the correct sensitivity of the intrauterine screening test.
A 8% B 80% C 87% D 92% E 99.9% how to solve something like this ? 
#2




Should give you this 2x2
80 7 100 99k which would mean sensitivity = 80/180 = 44%... which isn't an answer choice... but on second glance it says "100 of those originally screened were found to have the disease." This fact includes the 80 that we have up there... meaning the correct 2x2 is: 80 7 20 99k aka 80/100 = 80% sensitivity. 
#3




dang how do you know how to solve this so fast ?
tell me how to study this subject ? Quote:

#4




Just do a 2*2 table and fill the blanks with the info they gave u .
Total number of subjects is 100000 Total number of people tested positive 87  of which 80 are TP and 7 are FP if the total number is 100000 and 87 tested positive then it means (10000087) tested negative of which some are TN and others are FN He told u that 100 people have the disease (in total from all people tested) .. These 100 are divided into 80 (TP) + 20 (FN)(10080) Now u can easily calculate sensitivity which is 80/100 
#5




why is not TP 87 ???? why 80, how do make sure I do not make this errors ?
Total number of people tested positive 87  of which 80 are TP and 7 are FP Quote:

#6




in the question stem he tells you 87 ppl tested positive.. so this the total positives. Some of them will be TP and some will be FP
He has given u the FP directly in the question as 7 so FP=all positives FP If u draw the table from the beginning and just fill the blanks it will be easy without even considering what is TP and what is FP 
Thread Tools  Search this Thread 
Display Modes  

Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
Statistics question my brain friend can you solve this 2x2 table  ezguy  USMLE Step 1 Forum  1  05142015 09:06 PM 
How to solve this confidence interval question ?  ezguy  USMLE Step 1 Forum  7  05122015 08:48 PM 
How to solve this Aa gradient question?  JJacobs152  USMLE Step 1 Forum  8  06242013 03:15 AM 
Help me solve this NBME question please !  samaher  USMLE Step 1 Forum  0  03072012 08:07 PM 
A little tricky question to solve..  dr.Hanief  USMLE Step 1 Forum  7  07022011 12:51 PM 
