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Endgames Statistical Question

Non-parametric statistical tests for two independent groups: numerical data

BMJ 2014; 348 doi: (Published 25 April 2014) Cite this as: BMJ 2014;348:g2907
  1. Philip Sedgwick, reader in medical statistics and medical education
  1. 1Centre for Medical and Healthcare Education, St George’s, University of London, London, UK
  1. p.sedgwick{at}

Researchers described the outcomes at one year for a national cohort of infants with gastroschisis. A prospective cohort study design was used. Participants were 301 liveborn infants with gastroschisis between October 2006 and March 2008 from all 28 paediatric surgical centres in the United Kingdom and Ireland. The aim of the study was to describe outcomes at one year, comparing infants with simple gastroschisis (intact, uncompromised, and continuous bowel) with those with complex gastroschisis (bowel perforation, necrosis, or atresia). The main outcome measures included duration of parenteral nutrition and length of stay in hospital.1

The duration of parenteral nutrition and length of stay in hospital did not follow a normal distribution. Therefore, the groups of infants were compared using non-parametric statistical tests. Infants with complex gastroschisis had a significantly longer duration of parenteral nutrition than those with simple gastroschisis (median 51 days (interquartile range 29-92) v 23 days (16-38); P<0.001). Those with complex gastroschisis also needed a significantly longer stay in hospital (median 84 days (47-197) v 36 days (23-57); P<0.001).

The researchers concluded that the national cohort provided a benchmark against …

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