Education And Debate

Statistics Notes: Interaction 1: heterogeneity of effects

BMJ 1996; 313 doi: http://dx.doi.org/10.1136/bmj.313.7055.486 (Published 24 August 1996) Cite this as: BMJ 1996;313:486
  1. Douglas G Altman, heada,
  2. John N S Matthews, senior lecturer in medical statisticsb
  1. a ICRF Medical Statistics Group, Centre for Statistics in Medicine, Institute of Health Sciences, PO Box 777, Oxford OX3 7LF
  2. b Department of Medical Statistics, University of Newcastle, Newcastle upon Tyne NE2 4HH
  1. Correspondence to: Mr Altman.

    In several types of study we may want to examine the consistency of an observed relation across two or more subgroups of the individuals studied. For example, in a clinical trial we might want to know if the observed treatment difference is the same for young and old patients or for different stages of disease at presentation. In an epidemiological study we might want to know whether the observed relation between an exposure and disease is different among smokers and non-smokers

    In such cases we are interested in examining whether one effect is modified by the value of another variable. This may be viewed as the examination of the heterogeneity of an observed effect, such as treatment benefit in a clinical trial, across subsets of individuals. The statistical term for heterogeneity of this type is …

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