title: A computer program to estimate power and relative efficiency of flexibly matched case-control studies.
abstract: OBJECTIVE
  We recently introduced the concept of flexible matching strategies with varying proportions of a dichotomous matching factor among controls to increase power and efficiency of case-control studies. We now present a method and a computer program to calculate power and relative efficiency compared to an unmatched design varying the proportion of the matching factor in controls over all possible values from 0 to 100 percent.
  
  
  METHODS
  For all these values, the program calculates the expected variance of the combined Mantel-Haenszel odds ratio and determines the power using the standard error of the expected combined Mantel-Haenszel odds ratio under the null hypothesis as derived from the Mantel-Haenszel test statistic without continuity correction.
  
  
  RESULTS
  Thereby, the program allows estimating the optimal prevalence of the matching factor in selected controls for a given scenario which often differs from the prevalence in cases. It furthermore allows to estimate loss in power and efficiency compared to optimal matching by suboptimal matching.
  
  
  CONCLUSIONS
  Estimations like these are helpful with respect to the decision when to stop efforts to optimize the degree of matching during the recruitment of controls. Our program will strongly facilitate assessing the benefits of flexible matching strategies.
authors.affiliation: Department of Epidemiology, German Centre for Research on Ageing at the University of Heidelberg, Heidelberg, Germany. til.sturmer@post.harvard.edu
authors.forename: T
authors.initials: T
authors.lastname: Stürmer
authors.forename: O
authors.initials: O
authors.lastname: Gefeller
authors.forename: H
authors.initials: H
authors.lastname: Brenner
mesh_terms: D016022:Case-Control Studies; D016001:Confidence Intervals; D005858:Germany; D006801:Humans; D008432:Mathematical Computing; D015233:Models, Statistical