A pioneer study randomly assigned pregnant women to either a daily multivitamin supplement (including folic acid) or a placebo. In the 2104 pregnancies in the women taking the vitamin regimen, there were 28 cases of congenital malformation. In the 2052 pregnancies in the women taking the placebo, 47 cases of congenital malformation were recorded. Rounded to the nearest whole number, what is the number needed to treat, NNT, to prevent one congenital malformation when taking a multivitamin supplement compared with taking a placebo?

Question

Quizplus · Accepted Answer

The number needed to treat (NNT) is calculated as the inverse of the absolute risk reduction (ARR). ARR is the difference in the risk of congenital malformations between the placebo group and the treatment group. The risk in the treatment group is 28/2104, and the risk in the placebo group is 47/2052. The ARR is (47/2052) - (28/2104). Calculating this gives an ARR of approximately 0.0096. The NNT is 1/0.0096, which is approximately 104 when rounded to the nearest whole number.

A Pioneer Study Randomly Assigned Pregnant Women to Either a Daily