- Douglas G Altman, professor of statistics in medicine (email@example.com)1,
- J Martin Bland, professor of health statistics2
- 1 Cancer Research UK Medical Statistics Group, Centre for Statistics in Medicine, Oxford OX3 7LF,
- 2 Department of Health Sciences, University of York, York YO10 5DD
- Correspondence to: D Altman
In almost all controlled trials treatments are allocated by randomisation. Blocking and stratification can be used to ensure balance between groups in size and patient characteristics.1 But stratified randomisation using several variables is not effective in small trials. The only widely acceptable alternative approach is minimisation,2 3 a method of ensuring excellent balance between groups for several prognostic factors, even in small samples. With minimisation the treatment allocated to the next participant enrolled in the trial depends (wholly or partly) on the characteristics of those participants already enrolled. The aim is that each allocation should minimise the imbalance across multiple factors.
Table 1 shows some baseline characteristics in a controlled trial comparing two types of counselling in relation to dietary intake.4 Minimisation was used for the …