June 23, 2010

MRCP 1 Question 4

A random controlled trial of acute asthma treatment was performed in the emergency department wherein patients were discharged with oral corticosteroids plus either budesonide (an inhaled corticosteroid) or placebo.

The main outcome event was relapse, defined as an unscheduled visit for worsening asthma symptoms within 21 days of discharge.

Of the 100 patients randomized to budesonide, 25 relapsed. Conversely, 50 of the 94 patients randomized to placebo relapsed.

What is the relative reduction in 21-day relapse from asthma in the treated patients ?

a) 7.5%
b) 12.5%
c) 17.5%
d) 25%
e) 50%

The correct answer is E


The relative risk reduction (RRR) is a quantification of how much the treatment reduces the risk of the outcome relative to the baseline outcome event rate. Wherein the baseline risk of an outcome event is the event rate in the control group defined by C/(C + D), the RRR is the difference in outcome event rates between the control and treatment groups divided by the outcome event rate in the control group.

The relative risk reduction = (0.50 - 0.25) / 0.50 = 0.50

we convert these numbers to percent by simply multiplying by 100 to arrive at
The relative risk reduction = 50%

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