title: Application of zero-inflated poisson mixed models in prognostic factors of hepatitis C.
abstract: OBJECTIVE
  In recent years, hepatitis C virus (HCV) infection represents a major public health problem. Evaluation of risk factors is one of the solutions which help protect people from the infection. This study aims to employ zero-inflated Poisson mixed models to evaluate prognostic factors of hepatitis C.
  
  
  METHODS
  The data was collected from a longitudinal study during 2005-2010. First, mixed Poisson regression (PR) model was fitted to the data. Then, a mixed zero-inflated Poisson model was fitted with compound Poisson random effects. For evaluating the performance of the proposed mixed model, standard errors of estimators were compared.
  
  
  RESULTS
  The results obtained from mixed PR showed that genotype 3 and treatment protocol were statistically significant. Results of zero-inflated Poisson mixed model showed that age, sex, genotypes 2 and 3, the treatment protocol, and having risk factors had significant effects on viral load of HCV patients. Of these two models, the estimators of zero-inflated Poisson mixed model had the minimum standard errors.
  
  
  CONCLUSIONS
  The results showed that a mixed zero-inflated Poisson model was the almost best fit. The proposed model can capture serial dependence, additional overdispersion, and excess zeros in the longitudinal count data.
authors.affiliation: Department of Basic Sciences, School of Rehabilitation, Shahid Beheshti University of Medical Science, Tehran, Iran.
authors.forename: Alireza
authors.initials: A
authors.lastname: Akbarzadeh Baghban
authors.forename: Asma
authors.initials: A
authors.lastname: Pourhoseingholi
authors.forename: Farid
authors.initials: F
authors.lastname: Zayeri
authors.forename: Ali Akbar
authors.initials: AA
authors.lastname: Jafari
authors.forename: Seyed Moayed
authors.initials: SM
authors.lastname: Alavian
mesh_terms: D000328:Adult; D000368:Aged; D005260:Female; D016174:Hepacivirus / Q000235:genetics* / Q000472:pathogenicity; D006526:Hepatitis C / Q000188:drug therapy* / Q000453:epidemiology* / Q000473:pathology; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D015233:Models, Statistical; D016012:Poisson Distribution; D011379:Prognosis; D012307:Risk Factors