WBR0629: Difference between revisions
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{{WBRQuestion | {{WBRQuestion | ||
|QuestionAuthor={{ | |QuestionAuthor={{YD}} (Reviewed by {{YD}}) | ||
|ExamType=USMLE Step 1 | |ExamType=USMLE Step 1 | ||
|MainCategory=Biostatistics/Epidemiology | |MainCategory=Biostatistics/Epidemiology | ||
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|MainCategory=Biostatistics/Epidemiology | |MainCategory=Biostatistics/Epidemiology | ||
|SubCategory=Cardiology | |SubCategory=Cardiology | ||
|MainCategory=Biostatistics/Epidemiology | |||
|MainCategory=Biostatistics/Epidemiology | |MainCategory=Biostatistics/Epidemiology | ||
|MainCategory=Biostatistics/Epidemiology | |MainCategory=Biostatistics/Epidemiology | ||
Line 20: | Line 21: | ||
|MainCategory=Biostatistics/Epidemiology | |MainCategory=Biostatistics/Epidemiology | ||
|SubCategory=Cardiology | |SubCategory=Cardiology | ||
|Prompt=A study addresses the | |Prompt=A study addresses the secondary prevention of acute coronary syndrome (ACS) using a novel cholesterol-lowering agent. After 5 years, follow-up reveals recurrence of at least 1 ACS event among 200 out of 2000 subjects who were administered the novel agent vs. 540 out of 2400 subjects who were administered standard therapy. How many patients should be administered the novel agent to prevent at least 1 ACS event for 5 years? | ||
|Explanation=The [[number needed to treat]] (NNT) is an [[epidemiology|epidemiological]] measure that indicates how many patients would require treatment with a form of [[medication]] to reduce the expected number of cases of a defined endpoint by one. | |Explanation=The [[number needed to treat]] (NNT) is an [[epidemiology|epidemiological]] measure that indicates how many patients would require treatment with a form of [[medication]] to reduce the expected number of cases of a defined endpoint by one. It is defined as the inverse of the [[absolute risk reduction]]. In this vignette, the drug reduces the risk of recurrence of [[ACS]] from 22.5% to 10%. Therefore the absolute risk reduction is 12.5%. The NNT for a 5-year treatment with the novel cholesterol-lowering agent is the inverse of the absolute risk reduction, and it is 8%. | ||
Shown below is a detailed explanation of the calculation of NNT:<br> | Shown below is a detailed explanation of the calculation of NNT:<br> | ||
Rate of recurrence | Rate of ACS recurrence in the drug group: (200/2000)x100= 10%<br> | ||
Rate of recurrence | Rate of ACS recurrence in the placebo group: (540/2400)x100= 22.5%<br> | ||
Absolute risk reduction= 22.5%- 10%= 12.5%<br> | Absolute risk reduction= 22.5% - 10%= 12.5%<br> | ||
NNT= 1/0.125=8<br> | NNT= 1/0.125=8<br> | ||
|AnswerA=4 | |AnswerA=4 | ||
|AnswerAExp=This number is incorrect. | |AnswerAExp=This number is incorrect. | ||
|AnswerB=8 | |AnswerB=8 | ||
|AnswerBExp=In this | |AnswerBExp=In this vignette, the agent reduces the risk of ACS recurrence from 22.5% to 10%. Therefore the absolute risk reduction is 12.5%. A 5 The NNT for a 5-year treatment with the novel agent is the inverse of the [[absolute risk reduction]] is 1/0.125 = 0.08 = 8%. | ||
|AnswerC=16 | |AnswerC=16 | ||
|AnswerCExp=This number is incorrect. | |AnswerCExp=This number is incorrect. | ||
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|AnswerE=64 | |AnswerE=64 | ||
|AnswerEExp=This number is incorrect. | |AnswerEExp=This number is incorrect. | ||
|EducationalObjectives=The number need to treat (NNT) is defined as the number of patients who require treatment with a form of [[medication]] in order to reduce the expected number of cases of a defined endpoint by one. NNT is calculated as the inverse of the relative risk reduction. | |||
|References=First Aid 2014 page 53 | |||
|RightAnswer=B | |RightAnswer=B | ||
|WBRKeyword=Number needed to treat, NNT | |WBRKeyword=Number needed to treat, NNT, Relative risk reduction, RRR, Endpoint, ACS, Acute coronary syndrome | ||
|Approved=No | |Approved=No | ||
}} | }} |
Revision as of 16:33, 17 September 2014
Author | [[PageAuthor::Yazan Daaboul, M.D. (Reviewed by Yazan Daaboul, M.D.)]] |
---|---|
Exam Type | ExamType::USMLE Step 1 |
Main Category | MainCategory::Biostatistics/Epidemiology |
Sub Category | SubCategory::Cardiology |
Prompt | [[Prompt::A study addresses the secondary prevention of acute coronary syndrome (ACS) using a novel cholesterol-lowering agent. After 5 years, follow-up reveals recurrence of at least 1 ACS event among 200 out of 2000 subjects who were administered the novel agent vs. 540 out of 2400 subjects who were administered standard therapy. How many patients should be administered the novel agent to prevent at least 1 ACS event for 5 years?]] |
Answer A | AnswerA::4 |
Answer A Explanation | AnswerAExp::This number is incorrect. |
Answer B | AnswerB::8 |
Answer B Explanation | [[AnswerBExp::In this vignette, the agent reduces the risk of ACS recurrence from 22.5% to 10%. Therefore the absolute risk reduction is 12.5%. A 5 The NNT for a 5-year treatment with the novel agent is the inverse of the absolute risk reduction is 1/0.125 = 0.08 = 8%.]] |
Answer C | AnswerC::16 |
Answer C Explanation | AnswerCExp::This number is incorrect. |
Answer D | AnswerD::32 |
Answer D Explanation | AnswerDExp::This number is incorrect. |
Answer E | AnswerE::64 |
Answer E Explanation | AnswerEExp::This number is incorrect. |
Right Answer | RightAnswer::B |
Explanation | [[Explanation::The number needed to treat (NNT) is an epidemiological measure that indicates how many patients would require treatment with a form of medication to reduce the expected number of cases of a defined endpoint by one. It is defined as the inverse of the absolute risk reduction. In this vignette, the drug reduces the risk of recurrence of ACS from 22.5% to 10%. Therefore the absolute risk reduction is 12.5%. The NNT for a 5-year treatment with the novel cholesterol-lowering agent is the inverse of the absolute risk reduction, and it is 8%.
Shown below is a detailed explanation of the calculation of NNT: |
Approved | Approved::No |
Keyword | WBRKeyword::Number needed to treat, WBRKeyword::NNT, WBRKeyword::Relative risk reduction, WBRKeyword::RRR, WBRKeyword::Endpoint, WBRKeyword::ACS, WBRKeyword::Acute coronary syndrome |
Linked Question | Linked:: |
Order in Linked Questions | LinkedOrder:: |