title: Crossover or parallel design in infertility trials? The discussion continues.
abstract: OBJECTIVE
  To determine whether a crossover design results in a different estimate of treatment effect compared with a parallel design.
  
  
  METHODS
  With the aid of a computer program, data sets of subfertile patients were simulated under different assumptions. These patients were subjected to 2 treatments that were compared in either a parallel-design or a crossover-design trial. Results were analyzed using logistic regression.
  
  
  METHODS
  University hospital.
  
  
  METHODS
  Simulated patients of a heterogeneous subfertile population.
  
  
  METHODS
  Two treatment modalities with a pregnancy rate of 10% and of 20% in the first cycle were offered for 6 cycles to simulated heterogeneous populations.
  
  
  METHODS
  After 1,000 simulations for each assumption, median pregnancy rates and odds ratios were compared between the crossover- and parallel-design trials.
  
  
  RESULTS
  No relevant difference in estimated treatment effect was found between the designs. The crossover design resulted in more pregnancies overall than the parallel design.
  
  
  CONCLUSIONS
  In infertility research, parallel and crossover designs will lead to about the same results. Although the crossover design showed a slight tendency to overestimate the treatment effect of the most effective treatment, this overestimation is clinically not relevant and is small in relation to the random error. Because of its practical advantages and because more pregnancies are achieved, a crossover design should be the first choice in infertility research.
authors.affiliation: Department of Reproductive Medicine, University Hospital Utrecht, The Netherlands. B.COHLEN@DOG.AZU.NL
authors.forename: B J
authors.initials: BJ
authors.lastname: Cohlen
authors.forename: E R
authors.initials: ER
authors.lastname: te Velde
authors.forename: C W
authors.initials: CW
authors.lastname: Looman
authors.forename: R
authors.initials: R
authors.lastname: Eijckemans
authors.forename: J D
authors.initials: JD
authors.lastname: Habbema
mesh_terms: D003198:Computer Simulation; D018592:Cross-Over Studies; D005260:Female; D005298:Fertility / Q000502:physiology; D006801:Humans; D007246:Infertility / Q000628:therapy*; D008297:Male; D008597:Menstrual Cycle; D008962:Models, Theoretical; D016017:Odds Ratio; D011247:Pregnancy; D012107:Research Design