Re: Effectiveness of home based early intervention on children’s BMI at age 2: randomised controlled trial
Minor corrections are required for the description of the sample size calculation in our paper titled “Effectiveness of a home-based early intervention on children’s BMI at age two years: randomised controlled trial.” BMJ 2012;344:e3732. The revised text, which will have no effect on the overall results, should read as follows:
“The sample size calculation was based on the primary outcome, BMI or BMI z-score, which was assumed to have a SD of 1.5, or 1.0 respectively. To have 80% power to detect a difference in mean BMI of 0.38, or mean BMI z-score of 0.25 units between the groups at age 2 at the two sided 5% significance level, we needed a sample size of 252 per group.”
We reported the outcome in terms of BMI z-score in the responses to our paper at http://www.bmj.com/content/344/bmj.e3732?tab=responses
We sincerely apologise for this error.
Would you please also draw this to the attention of Philip Sedgwick, who used our article as an example in his paper “Sample size: how many participants are needed in a trial?” BMJ 2013;346:f1041.
Competing interests: No competing interests