WBR0629

Author	[[PageAuthor::Rim Halaby, M.D. [1]]]
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Biostatistics/ Epidemiology
Sub Category	SubCategory::Cardiology
Prompt	[[Prompt::A study addresses the use of a novel cholesterol lowering drug among patients with one or more previous episodes of acute coronary syndrome (ACS) for the prevention of the recurrence of ACS. Five year follow up reveals recurrence of ACS among 200 out of 2000 subjects who were administered the drug under investigation versus 540 out of 2400 subjects who were administered placebo. What is the number to treat for the novel drug during 5 years?]]
Answer A	AnswerA::4
Answer A Explanation	AnswerAExp::This number is incorrect.
Answer B	AnswerB::8
Answer B Explanation	[[AnswerBExp::In this question 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 drug is the inverse of the absolute risk reduction, and it is 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 question 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 drug is the inverse of the absolute risk reduction, and it is 8%. Shown below is a detailed explanation of the calculation of NNT: Rate of recurrence of ACS in the drug group: (200/2000)x100= 10% Rate of recurrence of ACS in the placebo group: (540/2400)x100= 22.5% Absolute risk reduction= 22.5%- 10%= 12.5% NNT= 1/0.125=8 Educational objective: The number need to treat (NNT) 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. NNT is calculated as the inverse of the relative risk reduction. Educational Objective: References: ]]
Approved	Approved::No
Keyword	WBRKeyword::Number needed to treat, WBRKeyword::NNT
Linked Question	Linked::
Order in Linked Questions	LinkedOrder::