title: Statistical Models of Parkinson's Disease Progression: Predictive Validity in a 3-Year Follow-up.
abstract: The rate of Parkinson's disease (PD) progression varies widely between patients. Current knowledge does not allow to accurately predict the evolution of symptoms in a given individual over time.
  
  
  
  To develop regression-based models of PD progression and to explore its predictive value in a three-year follow-up.
  
  
  
  At baseline, 300 consecutive PD patients were assessed using the Unified Parkinson's Disease Rating Scale (UPDRS) - subscales II and III, Hoehn & Yahr (H&Y) and Schwab and England Independence Scale (S&E); and the Freezing of Gait Questionnaire (FOG-Q). UPDRS-III and H&Y were applied in OFF and ON medication conditions. An axial index was derived from the UPDRS-III. Based on multiple linear regression coefficients, algorithms were developed to adjust test scores to the characteristics of each individual. Sixty-eight patients were reevaluated three years later.
  
  
  
  In the construction of the models, disease duration, age ≥70, age at disease onset ≥55, tremor as the first symptom alone, and medication description explained between 35% (UPDRS-III in ON) and 57% (axial index in ON) of the variance of test scores. The predictive r2 of the models in a 10-fold cross-validation ranged between 33% (UPDRS-III in ON) and 55% (axial index in ON and S&E in OFF). All measures, except UPDRS-III OFF, H&Y ON, and S&E ON, had moderate/good absolute agreement (intraclass correlation coefficient between 0.60 and 0.72) between baseline and follow-up.
  
  
  
  A cross-sectional assessment of a PD population allowed the development of models of disease progression, whose predictive value was validated on a three-year longitudinal study.
authors: Serviço de Neurologia, Centro Hospitalar do Porto, Porto, Portugal.|Unidade Multidisciplinar de Investigação Biomédica, Instituto Ciências Biomédicas Abel Salazar, Universidade do Porto, Porto, Portugal.
authors: Alexandre
authors: A
authors: Mendes
authors: Serviço de Neurologia, Centro Hospitalar do Porto, Porto, Portugal.|Unidade Multidisciplinar de Investigação Biomédica, Instituto Ciências Biomédicas Abel Salazar, Universidade do Porto, Porto, Portugal.
authors: Alexandra
authors: A
authors: Gonçalves
authors: Serviço de Neurologia, Centro Hospitalar do Porto, Porto, Portugal.|Faculdade de Medicina da Universidade do Porto, Porto, Portugal.
authors: Nuno
authors: N
authors: Vila-Chã
authors: Serviço de Neurologia, Centro Hospitalar do Porto, Porto, Portugal.
authors: Margarida
authors: M
authors: Calejo
authors: Unidade Multidisciplinar de Investigação Biomédica, Instituto Ciências Biomédicas Abel Salazar, Universidade do Porto, Porto, Portugal.
authors: Inês
authors: I
authors: Moreira
authors: Unidade Multidisciplinar de Investigação Biomédica, Instituto Ciências Biomédicas Abel Salazar, Universidade do Porto, Porto, Portugal.
authors: Joana
authors: J
authors: Fernandes
authors: Serviço de Neurologia, Centro Hospitalar do Porto, Porto, Portugal.
authors: Joana
authors: J
authors: Damásio
authors: Faculdade de Medicina da Universidade do Porto, Porto, Portugal.|CINTESIS, Faculdade de Medicina da Universidade do Porto, Porto, Portugal.|Sydney School of Public Health, University of Sydney, Sydney, Australia.
authors: Armando
authors: A
authors: Teixeira-Pinto
authors: Department of Clinical Neurosciences, Clinic of Neurology, Geneva University Hospital, Geneva, Switzerland.|Department of Basic Neurosciences, Medical Faculty, University of Geneva, Geneva, Switzerland.
authors: Paul
authors: P
authors: Krack
authors: Serviço de Neurologia, Centro Hospitalar do Porto, Porto, Portugal.
authors: António Bastos
authors: AB
authors: Lima
authors: Serviço de Neurologia, Centro Hospitalar do Porto, Porto, Portugal.|Unidade Multidisciplinar de Investigação Biomédica, Instituto Ciências Biomédicas Abel Salazar, Universidade do Porto, Porto, Portugal.
authors: Sara
authors: S
authors: Cavaco
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D003430:Cross-Sectional Studies; D018450:Disease Progression; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D008875:Middle Aged; D015233:Models, Statistical; D010300:Parkinson Disease / Q000175:diagnosis*; D011379:Prognosis; D015203:Reproducibility of Results
keywords: Parkinson disease; disease progression; statistical models; validity of results