UWorld Biostats ID: 1176

[OrthoRehab33]

I'm really struggling with this question and answer stem. I just can't wrap my head around it even though this should be easy. Anyone that can explain this to me like I'm 5- I'd really appreciate it!

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[zhopv10]

What's the stem?


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[OrthoRehab33]

What's the stem?


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A study is designed to evaluate the efficacy of a new drug, KM28. The study compares KM28 plus standard care verus standard care alone with regard to decreasing the incidence of recurrent breast cancer. The drug plus standard care will be approved if it decreases the rate of breast cancer recurrence by at least 40% compared to standard therapy alone. The reucrrence rate on standard therapy is 8%. In order to approve KM28, what's the maximal incidence of recurrent disease acceptable for women treated with KM28 plus standard therapy?

The answer is 4.8%

 

[TBV]

A study is designed to evaluate the efficacy of a new drug, KM28. The study compares KM28 plus standard care verus standard care alone with regard to decreasing the incidence of recurrent breast cancer. The drug plus standard care will be approved if it decreases the rate of breast cancer recurrence by at least 40% compared to standard therapy alone. The reucrrence rate on standard therapy is 8%. In order to approve KM28, what's the maximal incidence of recurrent disease acceptable for women treated with KM28 plus standard therapy?

The answer is 4.8%

0.4 x .08= .032

.08-.032=.048

.048x100= 4.8%

Or in words take 40% of 8% then subtract that number from the original 8%.

 

[dempty]

0.4 x .08= .032

.08-.032=.048

.048x100= 4.8%

You got it, but it might help to add a little more context (and show another approach, but either will work).

They're essentially asking for a minimum relative risk reduction of 40% (more or less). Think that RRR= 0.4 = 1-RR --- solve for RR which is 0.6. So, now you know 0.6 = (x/0.08); where x is the (maximum) recurrence rate in the treatment group --> multiply both sides by 0.08--- (0.08)*(0.6) = x = 0.048 or 4.8% is the maximum recurrence rate in the tx group. We know this is the maximum recurrence rate because any value above 0.048 will give us a relative risk of greater than 0.60 and a relative risk reduction of less than 0.40 (or if you recall how to work with inequalities, you could set it up that way, too).