title: Validation by simulation of a clinical trial model using the standardized mean and variance criteria.
abstract: OBJECTIVE
  To develop and validate a model of a clinical trial that evaluates the changes in cholesterol level as a surrogate marker for lipodystrophy in HIV subjects under alternative antiretroviral regimes, i.e., treatment with Protease Inhibitors vs. a combination of nevirapine and other antiretroviral drugs.
  
  
  METHODS
  Five simulation models were developed based on different assumptions, on treatment variability and pattern of cholesterol reduction over time. The last recorded cholesterol level, the difference from the baseline, the average difference from the baseline and level evolution, are the considered endpoints. Specific validation criteria based on a 10% minus or plus standardized distance in means and variances were used to compare the real and the simulated data.
  
  
  RESULTS
  The validity criterion was met by all models for considered endpoints. However, only two models met the validity criterion when all endpoints were considered. The model based on the assumption that within-subjects variability of cholesterol levels changes over time is the one that minimizes the validity criterion, standardized distance equal to or less than 1% minus or plus.
  
  
  CONCLUSIONS
  Simulation is a useful technique for calibration, estimation, and evaluation of models, which allows us to relax the often overly restrictive assumptions regarding parameters required by analytical approaches. The validity criterion can also be used to select the preferred model for design optimization, until additional data are obtained allowing an external validation of the model.
authors.affiliation: Universitat Politècnica de Catalunya, Facultat d'Informàtica, Laboratori de Càlcul, Barcelona, Spain. ismail.abbas@fib.upc.edu
authors.forename: Ismail
authors.initials: I
authors.lastname: Abbas
authors.forename: Joan
authors.initials: J
authors.lastname: Rovira
authors.forename: Josep
authors.initials: J
authors.lastname: Casanovas
mesh_terms: D044966:Anti-Retroviral Agents / Q000494:pharmacology; D002138:Calibration; D002784:Cholesterol / Q000378:metabolism; D002986:Clinical Trials as Topic / Q000379:methods*; D003198:Computer Simulation; D003627:Data Interpretation, Statistical; D006801:Humans; D008060:Lipodystrophy / Q000175:diagnosis*; D015233:Models, Statistical; D008962:Models, Theoretical; D019829:Nevirapine / Q000494:pharmacology; D011480:Protease Inhibitors / Q000494:pharmacology
chemical_list: D044966:Anti-Retroviral Agents; D011480:Protease Inhibitors; D002784:Cholesterol; D019829:Nevirapine