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{{WBRQuestion
{{WBRQuestion
|QuestionAuthor={{SSK}} (Reviewed by Serge Korjian and {{YD}})
|QuestionAuthor= {{SSK}} (Reviewed by Serge Korjian and {{YD}})
|ExamType=USMLE Step 1
|ExamType=USMLE Step 1
|MainCategory=Biostatistics/Epidemiology
|MainCategory=Biostatistics/Epidemiology
Line 22: Line 22:
|SubCategory=Gastrointestinal
|SubCategory=Gastrointestinal
|Prompt=A new vaccine is being developed for the prevention of Hepatitis E. In a phase 2 clinical trial, 100 individuals with negative Hepatitis E IgM and IgG anti-HEV antibodies are randomized to receive either the vaccine or placebo. Out of the 50 patients that received the vaccine, 1 went on to develop Hepatitis E in the 6 month follow-up after the vaccination. In the placebo group, 7 out of 50 patients developed Hepatitis E. What is the number needed to treat for this newly developed vaccine according to the results of this trial?
|Prompt=A new vaccine is being developed for the prevention of Hepatitis E. In a phase 2 clinical trial, 100 individuals with negative Hepatitis E IgM and IgG anti-HEV antibodies are randomized to receive either the vaccine or placebo. Out of the 50 patients that received the vaccine, 1 went on to develop Hepatitis E in the 6 month follow-up after the vaccination. In the placebo group, 7 out of 50 patients developed Hepatitis E. What is the number needed to treat for this newly developed vaccine according to the results of this trial?
|Explanation=The number needed to treat refers to the number of patients required to receive a certain treatment for 1 patient to benefit from it. It is usually the inverse of the absolute risk reduction(ARR). The ARR can be calculated as follows:
|Explanation=The [[number needed to treat]] (NNT) is an [[epidemiology|epidemiological]] measure that refers to the number of patients required to receive a certain treatment for 1 patient to benefit from it. It is the the inverse of the absolute risk reduction (ARR), where ARR is the absolute difference in the event rate between the treatment group (vaccine group) and the control group (placebo group). The ARR can be calculated as follows:


[[Image:ARRequation.jpg|600px]]
[[Image:ARRequation.jpg|800px]]
|AnswerA=0.14
 
|AnswerAExp=0.14 is not the number needed to treat
Shown below is a detailed explanation of the calculation of NNT:<br>
Rate of HEV development in the vaccine group: (1/50) x 100 = 2%<br>
Rate of HEV development in the placebo group: (7/50) x 100 = 14%<br>
Absolute risk reduction (ARR) = 14 - 2 = 12%  = 0.12
NNT = 1/0.12 = 8.33 patients
|AnswerA=1.14
|AnswerAExp=1.14 is not the number needed to treat
|AnswerB=7.14
|AnswerB=7.14
|AnswerBExp=7.14 is not the number needed to treat
|AnswerBExp=7.14 is not the number needed to treat
|AnswerC=8.33
|AnswerC=8.33
|AnswerCExp=The number needed to treat in this trial is 8.33
|AnswerCExp=The number needed to treat according to this trial is 8.33 patients
|AnswerD=300
|AnswerD=300
|AnswerDExp=300 is not the number needed to treat
|AnswerDExp=300 is not the number needed to treat
|AnswerE=Data insufficient to calculate
|AnswerE=Data insufficient to calculate
|AnswerEExp=Given the equation below, all variables are available to calculate the number needed to treat.
|AnswerEExp=Given the equation below, all variables are available to calculate the number needed to treat.
|EducationalObjectives=The number needed to treat is represents the inverse of the absolute risk reduction (1/ARR)
|EducationalObjectives=The [[number needed to treat]] (NNT) is an [[epidemiology|epidemiological]] measure that refers to the number of patients required to receive a certain treatment for 1 patient to benefit from it. NNT is defined as the inverse of the absolute risk reduction (1/ARR).
 
[[Image:ARRequation.jpg|800px]]
|References=First Aid 2014 page 53
|References=First Aid 2014 page 53
|RightAnswer=C
|RightAnswer=C
|WBRKeyword=Number needed to treat, Absolute risk reduction
|WBRKeyword=Number needed to treat, Absolute risk reduction, HEV, Trial, Vaccine, Placebo, NNT
|Approved=Yes
|Approved=Yes
|=12% = 0.12 <br>
NNT= 1/0.12 = 8.33 patients<br>
}}
}}

Latest revision as of 01:21, 28 October 2020
Author [[PageAuthor::Serge Korjian M.D. (Reviewed by Serge Korjian and Yazan Daaboul, M.D.)]]
Exam Type ExamType::USMLE Step 1
Main Category MainCategory::Biostatistics/Epidemiology
Sub Category SubCategory::Gastrointestinal
Prompt [[Prompt::A new vaccine is being developed for the prevention of Hepatitis E. In a phase 2 clinical trial, 100 individuals with negative Hepatitis E IgM and IgG anti-HEV antibodies are randomized to receive either the vaccine or placebo. Out of the 50 patients that received the vaccine, 1 went on to develop Hepatitis E in the 6 month follow-up after the vaccination. In the placebo group, 7 out of 50 patients developed Hepatitis E. What is the number needed to treat for this newly developed vaccine according to the results of this trial?]]
Answer A AnswerA::1.14
Answer A Explanation AnswerAExp::1.14 is not the number needed to treat
Answer B AnswerB::7.14
Answer B Explanation AnswerBExp::7.14 is not the number needed to treat
Answer C AnswerC::8.33
Answer C Explanation AnswerCExp::The number needed to treat according to this trial is 8.33 patients
Answer D AnswerD::300
Answer D Explanation AnswerDExp::300 is not the number needed to treat
Answer E AnswerE::Data insufficient to calculate
Answer E Explanation AnswerEExp::Given the equation below, all variables are available to calculate the number needed to treat.
Right Answer RightAnswer::C
Explanation [[Explanation::The number needed to treat (NNT) is an epidemiological measure that refers to the number of patients required to receive a certain treatment for 1 patient to benefit from it. It is the the inverse of the absolute risk reduction (ARR), where ARR is the absolute difference in the event rate between the treatment group (vaccine group) and the control group (placebo group). The ARR can be calculated as follows:

Shown below is a detailed explanation of the calculation of NNT:
Rate of HEV development in the vaccine group: (1/50) x 100 = 2%
Rate of HEV development in the placebo group: (7/50) x 100 = 14%
Absolute risk reduction (ARR) = 14 - 2 = 12% = 0.12 NNT = 1/0.12 = 8.33 patients
Educational Objective: The number needed to treat (NNT) is an epidemiological measure that refers to the number of patients required to receive a certain treatment for 1 patient to benefit from it. NNT is defined as the inverse of the absolute risk reduction (1/ARR).


References: First Aid 2014 page 53]]

Approved Approved::Yes
Keyword WBRKeyword::Number needed to treat, WBRKeyword::Absolute risk reduction, WBRKeyword::HEV, WBRKeyword::Trial, WBRKeyword::Vaccine, WBRKeyword::Placebo, WBRKeyword::NNT
Linked Question Linked::
Order in Linked Questions LinkedOrder::
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