Intended for healthcare professionals

Endgames Statistical Question

Clinical trials: outcome measures

BMJ 2015; 350 doi: (Published 12 January 2015) Cite this as: BMJ 2015;350:h121
  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}

Researchers investigated the effects of household based treatment of drinking water on the prevalence of diarrhoea in areas with a turbid water source in rural western Kenya.1 A cluster randomised controlled trial was performed. The intervention was water treatment with flocculant-disinfectant or sodium hypochlorite for 20 weeks. The control treatment was standard practice. In total, 605 family compounds, each with at least one child aged under 2 years and containing several houses, were recruited. Compounds were randomised to treatment using cluster allocation, stratified by the site of the main source of household water (pond water or river water). In total, 201 compounds (2124 people) were allocated to water treatment with flocculant-disinfectant, 203 compounds (2249) were allocated to sodium hypochlorite, and 201 compounds (2277) were allocated to control.

The primary outcome was the prevalence of diarrhoea. Secondary outcomes included all cause mortality, bacteriological (Escherichia coli) concentration, free residual chlorine concentration, and turbidity. The researchers reported that for all age groups combined, when compared with control, the prevalence of diarrhoea was significantly lower in the flocculant-disinfectant and sodium hypochlorite treatment groups. The number of deaths in each of the flocculant-disinfectant and sodium hypochlorite treatment groups did not differ significantly from the control group. Drinking water from intervention households was more likely than water from control households to meet World Health Organization guidelines for bacteriological quality. Furthermore, drinking water from flocculant-disinfectant households had much lower turbidity than samples from control or sodium hypochlorite households. There was no indication of improvement in water quality as measured by free residual chlorine concentration. It was concluded that flocculant-disinfectant is well suited as a household based …

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