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# Non inferiority margins Watch

1. Please can someone explain what the following block of text means. Why did they choose 6% as there non-inferoirty margin? thanks

"We followed CONSORT guidelines for conducting and reporting a non-inferiority study [23]. We designed the non-inferiority study with a 6% absolute risk difference as our non-inferiority margin (ΔNI). We selected the non-inferiority margin of 6% based on prior data comparing oxytocin with placebo for active management of labor that demonstrated a 50% relative reduction in the rate of PPH with oxytocin versus placebo [24]. Assuming a predicted incidence of PPH of 14% in mothers treated with prophylactic oxytocin, as reported previously by a well-powered clinical trial [15], a non-inferiority margin of 6% would correspond to an upper bound of PPH incidence of 20% among mothers treated with misoprostol. We chose this upper bound of non-inferiority so that a 20% PPH rate in the misoprostol arm would be similar to the rate for women treated with oxytocin and likely superior to predicted rates of PPH in women not receiving treatment"

PPH = post partum haemorrage (it is a condition of blood loss experiernced by women following birth).

The full paper is here: http://www.plosmedicine.org/article/...l.pmed.1001752

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Updated: December 27, 2014
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