title: Unequal randomisation can improve the economic efficiency of clinical trials.
abstract: OBJECTIVE
  In the majority of clinical trials patients are randomised equally between treatment groups. This approach maximises statistical power for a given total sample size. The objectives of this paper were to determine if, when research costs between treatments differ, it is more economically efficient to randomise additional patients to the cheaper treatment, and how the optimum randomisation ratio can be estimated.
  
  
  METHODS
  Estimation of the most economically efficient randomisation ratio for four hypothetical clinical trials using cost-effectiveness analysis.
  
  
  RESULTS
  When research costs differ between treatments, and there is no constraint on total sample size, it is always more cost-effective to randomise more patients to the cheaper treatment. For example, a cost ratio between the lesser and more expensive treatment of ten, results in a randomisation ratio of 3.2:1.
  
  
  CONCLUSIONS
  Unequal randomisation ratios should be more widely used as this will achieve optimum statistical power for the lowest expenditure of research resources.
authors.affiliation: Centre for Health Economics, University of York.
authors.forename: D
authors.initials: D
authors.lastname: Torgerson
authors.forename: M
authors.initials: M
authors.lastname: Campbell
mesh_terms: D002017:Budgets; D003362:Cost-Benefit Analysis; D003627:Data Interpretation, Statistical; D017598:Efficiency, Organizational / Q000191:economics; D010934:Planning Techniques; D016032:Randomized Controlled Trials as Topic / Q000191:economics* / Q000379:methods; D012107:Research Design; D012109:Research Support as Topic; D013222:State Medicine; D006113:United Kingdom