








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




Biostat question for the day
A research group is studying sickle cell disease in a geographically isolated community of 6000 people. A genetic analysis is performed on every community member. At the beginning of the year, it is determined that 10% are homozygous for hemoglobin S and therefore have sickle cell disease, and 30% of the community is heterozygous for the mutant allele. Over the course of the year, 100 infants are born, six of whom are diagnosed with sickle cell disease. Of the 80 people who die during the year, three had sickle cell disease.
Which of the following is the current incidence rate of sickle cell disease in this population? A. 6/3600 B. 6/100 C. 6/5400 D. 603/6020 E. 6/3620 F. 6/5420
__________________
In USMLE, “Any fool can know. The point is to understand.” 
#2




shudnt it b 6/6020..?
though of course der s no such option there..! 6 new cases andtotal population 6000+(10080) 
#3




Obviously ones its not there, u got to take another answer!
__________________
In USMLE, “Any fool can know. The point is to understand.” 
#4




D. 603/6020

#5




My answer is EE
Thanks for the question 
#6




It's tricky guys. More answers! You are all doing very well.
__________________
In USMLE, “Any fool can know. The point is to understand.” 
#7




Quote:
Now, 100 are born but 6 had SCD. so we add 94 to the denominator. 80 died but 3 had SCD. So we substract 77 from denominator So my denominator is 6000  2400 +94 77 = 3617 Numerator is 6 I donno what am I missing here 
The above post was thanked by:  
nsesereso (09232014) 
#8




Quote:

#9




My answer is AA

#10




Your reasoning pattern is excellent!
U got the concepts right. But u are just a little bit from the answer? Am impressed. U know its not acquired but u picked wrong answer!
__________________
In USMLE, “Any fool can know. The point is to understand.” 
The above post was thanked by:  
DrNewB (09232014) 
#11




Answer
Quote:
Incidence rate = No. of new cases in a year/ population at risk in that year No. of new cases = 6 (Because 6 infants with sickle cell disease is born) To calculate population at risk ... Firstly, Total population  People with sickle cell disease = 6000  600 = 5400 Secondly, 540 + No. of newly born infants in that year = 5400 + 100 = 5500 Then, 640 No. of total death in the year = 5500  100 = 5420 Therefore, total population at risk = 5420 Lastly, Incidence rate = 6/5420 
#12




Oops... I think that I have got wrong in my previous answer.
The correct answer should be "B". Because only the newborn infants are at risk. Is it true? 
#13




It's urx question which I modified a little bit.
Yea answer is B. Prevalence is commonly confused with incidence, which is the number of new cases in a unit of time divided by the number of susceptible people. Choice B represents the incidence of sickle cell disease during the year, Because the genotype of all community members is already known, only newborn infants are truly at risk for the disease. Therefore, of the 100 people at risk for sickle cell disease, 6 were diagnosed, yielding an incidence of 6/100. The prevalence is 603/6020
__________________
In USMLE, “Any fool can know. The point is to understand.” 
The above post was thanked by:  
dr_marini (09232014), Dr.ann (09232014), DrNewB (09232014), jeniaz (09232014), shaarang_93 (09232014) 
#15




Oh no i m late just seen the question but i would choose B too
Cuz 100 are at risk this year 6 are the new cases. In the last two lines the clearly mentioned this year so it means they are talking about the current incidence means this year incidence cuz rest will be prevelance. I tackle this type of question before not the same but kind is same. They confuse us with alot of numbers distractors. 
The above post was thanked by:  
nsesereso (09242014) 
#16




Quote:
__________________
In USMLE, “Any fool can know. The point is to understand.” 
Thread Tools  Search this Thread 
Display Modes  

Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
BioStat Question for Today  drpisho  USMLE Step 1 Forum  7  04012016 02:01 AM 
Biostat question for the day  nsesereso  USMLE Step 1 Forum  16  10122014 05:50 AM 
Biostat Question UWSA1  drpisho  USMLE Step 1 Forum  2  05192014 12:46 PM 
BioStat Question for Today  2  drpisho  USMLE Step 1 Forum  3  04292014 12:22 PM 
BioStat Question for Today  drpisho  USMLE Step 1 Forum  5  04282014 02:14 PM 
