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      Simple sample size calculation for cluster-randomized trials

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      International Journal of Epidemiology

      Oxford University Press (OUP)

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          Abstract

          Cluster-randomized trials, in which health interventions are allocated randomly to intact clusters or communities rather than to individual subjects, are increasingly being used to evaluate disease control strategies both in industrialized and in developing countries. Sample size computations for such trials need to take into account between-cluster variation, but field epidemiologists find it difficult to obtain simple guidance on such procedures. In this paper, we provide simple formulae for sample size determination for both unmatched and pair-matched trials. Outcomes considered include rates per person-year, proportions and means. For simplicity, formulae are expressed in terms of the coefficient of variation (SD/mean) of cluster rates, proportions or means. Guidance is also given on the estimation of this value, with or without the use of prior data on between-cluster variation. The methods are illustrated using two case studies: an unmatched trial of the impact of impregnated bednets on child mortality in Kenya, and a pair-matched trial of improved sexually-transmitted disease (STD) treatment services for HIV prevention in Tanzania.

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          Author and article information

          Journal
          International Journal of Epidemiology
          International Journal of Epidemiology
          Oxford University Press (OUP)
          0300-5771
          1464-3685
          April 01 1999
          April 01 1999
          : 28
          : 2
          : 319-326
          Article
          10.1093/ije/28.2.319
          10342698
          © 1999

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