Tawa

Critical appraisal

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A meta-analysis of antipsychotic related diabetes suggests that first generation antipsychotics reduce the relative risk of diabetes by around 25% in comaprison to second generation antipsychotics. You have a 32 year old man requiring antipsychotic prescription; with BMI <25 and no family history of diabetes, the risk of developing diabetes in next one year may be as low as 0.5% in this patient. How many such patients must be given first generation antipsychotic instead of second generation agent to prevent one case of diabetes

A.25

B.800

C.125

D.2

E.100

 

kindly explain the calculation .

 

 

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Answer : 800

It is asking about NNT

Reduction of Relative Risk : Absolute Risk Reduction (ARR) : 25% = 0.25

NNT : 1/ARR  = 4

However, translating this NNT to the specific patient : NNT/F

F:  estimate's patient risk : 0.5% = 0.005

New NNT = 4/ 0.005 = 800

 

Edited by Carole
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OTHER WAY COULD BE :

NNT PATIENT=  1/ PEER * RRR

PEER = 25%

RRR = 1 -RR = 0.5%

NNT PATIENT = 800

NNT:  Calculation of the number of patients one needs to treat (NNT) in order to prevent one patient from having the adverse event. However, here the question can be understood also as NNH. It depends on what approach you use. 

 

Edited by Carole

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thanks

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Thanks for simplified explanation

 

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Which is the best book to learn critical appraisal? I am looking for a theory based book rather than the Q&A form.

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Best book is The Doctor’s Guide to critical Appraisal by Gosall if you learn and understand this it’s more than enough to pass this part of the exam

Edited by SamMak
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