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a screening program in institute for detection of vaginal clamydia tracomis among first year women college students.at the initial screening evidence of clamydia tracomatis infection is founf in 500 of 2500 student .one year later evidence of C tramotis is found in an additional 200 students which of the following is anual incidence of c tracomatis infection in this population of students
A 8%
B10 %
c 16 %
d20%
e28 %
 

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a screening program in institute for detection of vaginal clamydia tracomis among first year women college students.at the initial screening evidence of clamydia tracomatis infection is founf in 500 of 2500 student .one year later evidence of C tramotis is found in an additional 200 students which of the following is anual incidence of c tracomatis infection in this population of students
A 8%
B10 %
c 16 %
d20%
e28 %
Incidence is the number of new cases per population in a specified time (usually a year, and here specifically asked as annually).

There are 200 new cases in following year out of the population of 2500 students. 200/2500 = .08; A

The population of students should remain 2500 because this is an acute condition that when found in a screening program like this would be treated. Those that had C trachomatis treated, would be free to contract it again.
 

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answer is B. 200/2000 = 10%. 500 are not included in group of risk.
Sure they are. If it were a chronic condition like HIV, then you would remove them from the at risk group.

From the CDC website:

When calculating the number of prevalent and incident infections, only those infections that were sexually transmitted were counted. In general, CDC estimated the total number of infections in the calendar year, rather than the number of individuals with infection, since one person can have more than one STI at a given time (e.g., HPV and chlamydia) or more than one episode of a single STI (e.g., repeat chlamydia infection).
 

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Discussion Starter · #28 ·
There is no info about how much students have got the treatment.

In this case right answer is B. It was correct in my NBME 16.

I want to ask USMLE1, does this question duplicated word to word?
 

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There is no info about how much students have got the treatment.

In this case right answer is B. It was correct in my NBME 16.

I want to ask USMLE1, does this question duplicated word to word?
There are many assumptions that we have to make when answering these questions. If I read about a university screening program for a STI, I am going to assume they get treated.

However, you guys are right according to NBME, the answer is 10%...but IMO only because of the word 'additional' before students. I guess this would imply that the 500 are being removed from the population. If it just said 200 students showed evidence of infection, you would have to include the original 500.
 

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Incidence is the number of new cases per population in a specified time (usually a year, and here specifically asked as annually).

There are 200 new cases in following year out of the population of 2500 students. 200/2500 = .08; A

The population of students should remain 2500 because this is an acute condition that when found in a screening program like this would be treated. Those that had C trachomatis treated, would be free to contract it again.
i choose A but it was wrong !! so i guess answer is 10 % new cases 200/2500-500= 10
 

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Discussion Starter · #31 ·
You can't add earlier positive-tested individuals in group of risk - they will harm incidence "statistical significance". Earlier positive-tested shouldn't be tested again. How can you distinguish between bad treatment or new infection in this group? They will injure the study and so cannot be included.

There are many assumptions that we have to make when answering these questions. If I read about a university screening program for a STI, I am going to assume they get treated.

However, you guys are right according to NBME, the answer is 10%...but IMO only because of the word 'additional' before students. I guess this would imply that the 500 are being removed from the population. If it just said 200 students showed evidence of infection, you would have to include the original 500.
 

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There is no info about how much students have got the treatment.

In this case right answer is B. It was correct in my NBME 16.

I want to ask USMLE1, does this question duplicated word to word?
yes it was and answer is 10% new cases are 200 we have subtract old ones from the population 2500-500 =2000
200/2000=10 % incidence
 

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There is no info about how much students have got the treatment.

In this case right answer is B. It was correct in my NBME 16.

I want to ask USMLE1, does this question duplicated word to word?
what about absolute risk reduction one .i got that one wrong too if u can solve it please?
 

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a new antiplatlet agent is developed for the prevention of recurrence of strokein a large randomized clinical trial with equal numbers of men and women the rates of a stroke are lower in patients recieving the new agentsthan in patient recieving the standard treatment
ecurrent stroke rates per 1000 person .years
standard treatment new antiplatlet
women .12 .04
men .24 .08
overall .18 .06
absolute risk reduction in women is 8%,12%,16% 33% 50% 62% 67% 75%
 

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Discussion Starter · #39 ·
wiki: the absolute risk reduction (risk difference or excess risk) is the change in risk of a given activity or treatment in relation to a control activity or treatment.
FA-2014: The difference in risk (not the proportion) attributable to the intervention as compared to a control (e.g., if 8% of people who receive a placebo vaccine develop flu vs. 2% of people who receive a flu vaccine, then
ARR = 8% − 2% = 6% = .06).
 

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wiki: the absolute risk reduction (risk difference or excess risk) is the change in risk of a given activity or treatment in relation to a control activity or treatment.
FA-2014: The difference in risk (not the proportion) attributable to the intervention as compared to a control (e.g., if 8% of people who receive a placebo vaccine develop flu vs. 2% of people who receive a flu vaccine, then
ARR = 8% − 2% = 6% = .06).
thanks and how do you differentiate between RRR relative reduction and absolute risk reduction i cant understand the explanation of these two given in FA 2014 and uworld ??
 
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