title: How to test validity in orthodontic research: a mixed dentition analysis example.
abstract: BACKGROUND
  The data used to test the validity of a prediction method should be different from the data used to generate the prediction model. In this study, we explored whether an independent data set is mandatory for testing the validity of a new prediction method and how validity can be tested without independent new data.
  
  
  METHODS
  Several validation methods were compared in an example using the data from a mixed dentition analysis with a regression model. The validation errors of real mixed dentition analysis data and simulation data were analyzed for increasingly large data sets.
  
  
  RESULTS
  The validation results of both the real and the simulation studies demonstrated that the leave-1-out cross-validation method had the smallest errors. The largest errors occurred in the traditional simple validation method. The differences between the validation methods diminished as the sample size increased.
  
  
  CONCLUSIONS
  The leave-1-out cross-validation method seems to be an optimal validation method for improving the prediction accuracy in a data set with limited sample sizes.
authors: Clinical assistant professor, Department of Orthodontics, College of Dentistry, University of Florida, Gainesville, Fla.
authors: Richard E
authors: RE
authors: Donatelli
authors: Professor and chair, Department of Orthodontics and Dental Research Institute, School of Dentistry, Seoul National University, Seoul, Korea. Electronic address: nonext@snu.ac.kr.
authors: Shin-Jae
authors: SJ
authors: Lee
mesh_terms: D000465:Algorithms; D001641:Bicuspid / Q000033:anatomy & histology; D003481:Cuspid / Q000033:anatomy & histology; D018865:Dental Research / Q000706:statistics & numerical data*; D003818:Dentition, Mixed; D005260:Female; D005544:Forecasting; D006801:Humans; D007180:Incisor / Q000033:anatomy & histology; D008297:Male; D015233:Models, Statistical; D009811:Odontometry / Q000706:statistics & numerical data; D009970:Orthodontics / Q000706:statistics & numerical data*; D012044:Regression Analysis; D015203:Reproducibility of Results; D018401:Sample Size; D012737:Sex Factors