Page 39 - PCC13

Expressing RR, OR and RD
• Risk ratio 1.25
– treatment increased the live birth rate by 25%
• Odds ratio 1.5
– the odds of a live birth in treated patients were about
1.5 times of what they were in controls
• Risk difference 10%
– Treatment increased the risk of a live birth by 10% points compared to a control rate of 40%
Number needed to treat
NNT is calculated by taking the reciprocal of the absolute difference between experimental groups.
Another way is by dividing 100 by absolute risk difference.
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PRECONGRESS COURSE 13 I BARCELONA, SPAIN – 1 JULY 2018 39