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In Reply Dr Bhaskaran and colleagues suggest that the interpretation of our study should be less dependent on the P value of .051, while Drs Merenstein and D’Amico suggest it should be more strict. We agree with Bhaskaran and colleagues that the 6.1% lower incidence of asthma and recurrent wheeze in the offspring with prenatal vitamin D supplementation may be better understood by considering the 95% CI.1 The relative risk reduction was 20% (HR, 0.8) and the CI suggested that the effect of the intervention is likely to lie between a 40% reduction and no reduction (95% CI, 0.6-1.0). However, a misconception is that the true effect can lie with equal likelihood throughout the estimated CI, when in fact it lies with a greater likelihood around the 20% estimate than the extremes of the CI distribution.1
Litonjua AA, Weiss ST. Prenatal Vitamin D and Offspring Wheezing—Reply. JAMA. 2016;315(24):2731. doi:10.1001/jama.2016.4121