Intended for healthcare professionals

Endgames Statistical Question

Pitfalls of statistical hypothesis testing: multiple testing

BMJ 2014; 349 doi: (Published 29 August 2014) Cite this as: BMJ 2014;349:g5310
  1. Philip Sedgwick, reader in medical statistics and medical education1
  1. 1Institute for Medical and Biomedical Education, St George’s, University of London, London, UK
  1. p.sedgwick{at}

The effectiveness of a home based intervention on children’s body mass index (BMI) at age 2 years was investigated. A randomised controlled superiority trial was used. The intervention consisted of eight home visits from specially trained community nurses in the first 24 months after birth. The aim of the intervention was to improve the health and wellbeing of parents and children. The intervention was in addition to the usual childhood nursing service from community health service nurses. The control group received the usual childhood nursing service alone. Participants were first time mothers and their infants.1

The primary outcome measures were children’s anthropometric measures, including BMI, weight, and length, at age 2 years. Secondary outcomes comprised eight measures of dietary behaviour and four measures of physical activity and television watching for the child at age 2 years. These included eating habits (intake of fruit and vegetables, consumption of chips and snacks), having a meal in front of the TV, time spent watching TV, and active play time. Secondary outcomes also included seven measures of dietary behaviour, time spent watching TV, and physical activity for the mother 24 months after giving birth.

It was reported that mean BMI at age 2 years was significantly lower in the intervention group than in the control group (P=0.04). At 24 months after birth, dietary behaviours and TV watching were significantly different for children in the intervention group compared with the control group. Children in the intervention group ate more vegetables (P=0.03), whereas using food as a reward (P=0.03), TV being on during mealtimes (P=0.02), eating dinner in front of the TV (P=0.01), and watching TV for more …

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