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#1
03-02-2016
 USMLE Forums Scout Steps History: Not yet Posts: 31 Threads: 18 Thanked 2 Times in 2 Posts Reputation: 12
relative risk reduction

you are designing a study to evaluate efficacy of new drug km28. your study will compare km28 plus standard care vs standard care alone in decreasing the incidence of recurrent breast cancer. the FDA will approve the new drug if km28 plus standard care reduces the rate of breast cancer recurrence by 40% compared to standard therapy alone. the recurrence rate on standard therapy is found to be 8%. in order for km28 to be approved, what is the maximal incidence of recurrent disease acceptable for women treated with km28 plus standard therapy?
A. 5.2%
B. 4.8%
C. 3.6%
D. 3.2%
E. 2.8%

guys i am not understanding how the relative risk reduction formula is applied here and what is relative risk reduction? can someone explain in detail??

#2
03-02-2016
 USMLE Forums Scout Steps History: Not yet Posts: 84 Threads: 1 Thanked 49 Times in 35 Posts Reputation: 59

Quote:
 Originally Posted by anamta you are designing a study to evaluate efficacy of new drug km28. your study will compare km28 plus standard care vs standard care alone in decreasing the incidence of recurrent breast cancer. the FDA will approve the new drug if km28 plus standard care reduces the rate of breast cancer recurrence by 40% compared to standard therapy alone. the recurrence rate on standard therapy is found to be 8%. in order for km28 to be approved, what is the maximal incidence of recurrent disease acceptable for women treated with km28 plus standard therapy? A. 5.2% B. 4.8% C. 3.6% D. 3.2% E. 2.8% guys i am not understanding how the relative risk reduction formula is applied here and what is relative risk reduction? can someone explain in detail??
You do not have to use the formula if you do not want to. You calculate 40% of 8=3.2% and then subtract 3.2 from 8=4.8%

That would give you a number which is 40% less than 8, which is what they are asking.

You can use the formula where RRR=1-RR.

RRR=40%=0.4
RR=new drug+standard of care/standard of care=x/8
You do not have to use 0.08 instead of 8% in the RR equation since it has no effect on the ratio as long as you keep in mind that the answer you get will also be in percentages.

0.6=x/8
x=8*0.6
x=4.8

You can see how much more calculations you have to do if you decide to go with the formula as opposed to reasoning it out yourself. On some of those questions formulas are more time consuming. Although, if you have the time it is always better to use the formula to double check your reasoning.

Relative risk reduction just says what percentages of cases you prevented (or cured, or whatever) with your intervention.
 The above post was thanked by: anamta (03-03-2016)
#3
03-03-2016
 USMLE Forums Scout Steps History: Not yet Posts: 31 Threads: 18 Thanked 2 Times in 2 Posts Reputation: 12

thanks nodo
#4
04-01-2016
 USMLE Forums Veteran Steps History: 1+CK+CS+3 Posts: 255 Threads: 26 Thanked 85 Times in 71 Posts Reputation: 95

Quote:
 Originally Posted by anamta you are designing a study to evaluate efficacy of new drug km28. your study will compare km28 plus standard care vs standard care alone in decreasing the incidence of recurrent breast cancer. the FDA will approve the new drug if km28 plus standard care reduces the rate of breast cancer recurrence by 40% compared to standard therapy alone. the recurrence rate on standard therapy is found to be 8%. in order for km28 to be approved, what is the maximal incidence of recurrent disease acceptable for women treated with km28 plus standard therapy? A. 5.2% B. 4.8% C. 3.6% D. 3.2% E. 2.8% guys i am not understanding how the relative risk reduction formula is applied here and what is relative risk reduction? can someone explain in detail??
Relative risk reduction is the decrease in incidence of a condition in one treatment group in comparison to another. In this question, you are given the relative risk reduction (40%) and the incidence of breast cancer in people on standard therapy (8%). What you need to do is enter the data into the equation for relative risk reduction and then solve for the incidence of breast cancer in the group of patients receiving km28.

Relative Risk Reduction = 1 - (Incidence in Group A / Incidence in Group B)
Relative Risk Reduction = 1 - [(A/A+B) / (C/C+D)]
40% = 1 - [(A/A+B) / 8%]
A/A+B = 60% * 8%
A/A+B = 4.8%
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