title: Systematic investigation of gastrointestinal diseases in China (SILC): validation of survey methodology.
abstract: BACKGROUND
  Symptom-based surveys suggest that the prevalence of gastrointestinal diseases is lower in China than in Western countries. The aim of this study was to validate a methodology for the epidemiological investigation of gastrointestinal symptoms and endoscopic findings in China.
  
  
  METHODS
  A randomized, stratified, multi-stage sampling methodology was used to select 18,000 adults aged 18-80 years from Shanghai, Beijing, Xi'an, Wuhan and Guangzhou. Participants from Shanghai were invited to provide blood samples and undergo upper gastrointestinal endoscopy. All participants completed Chinese versions of the Reflux Disease Questionnaire (RDQ) and the modified Rome II questionnaire; 20% were also invited to complete the 36-item Short Form Health Survey (SF-36) and Epworth Sleepiness Scale (ESS). The psychometric properties of the questionnaires were evaluated statistically.
  
  
  RESULTS
  The study was completed by 16,091 individuals (response rate: 89.4%), with 3219 (89.4% of those invited) completing the SF-36 and ESS. All 3153 participants in Shanghai provided blood samples and 1030 (32.7%) underwent endoscopy. Cronbach's alpha coefficients were 0.89, 0.89, 0.80 and 0.91, respectively, for the RDQ, modified Rome II questionnaire, ESS and SF-36, supporting internal consistency. Factor analysis supported construct validity of all questionnaire dimensions except SF-36 psychosocial dimensions.
  
  
  CONCLUSIONS
  This population-based study has great potential to characterize the relationship between gastrointestinal symptoms and endoscopic findings in China.
authors.affiliation: Department of Health Statistics, Second Military Medical University, Shanghai, China. xiaoyan1981@gmail.com
authors.forename: Xiaoyan
authors.initials: X
authors.lastname: Yan
authors.forename: Rui
authors.initials: R
authors.lastname: Wang
authors.forename: Yanfang
authors.initials: Y
authors.lastname: Zhao
authors.forename: Xiuqiang
authors.initials: X
authors.lastname: Ma
authors.forename: Jiqian
authors.initials: J
authors.lastname: Fang
authors.forename: Hong
authors.initials: H
authors.lastname: Yan
authors.forename: Xiaoping
authors.initials: X
authors.lastname: Kang
authors.forename: Ping
authors.initials: P
authors.lastname: Yin
authors.forename: Yuantao
authors.initials: Y
authors.lastname: Hao
authors.forename: Qiang
authors.initials: Q
authors.lastname: Li
authors.forename: John
authors.initials: J
authors.lastname: Dent
authors.forename: Joseph
authors.initials: J
authors.lastname: Sung
authors.forename: Duowu
authors.initials: D
authors.lastname: Zou
authors.forename: Saga
authors.initials: S
authors.lastname: Johansson
authors.forename: Katarina
authors.initials: K
authors.lastname: Halling
authors.forename: Wenbin
authors.initials: W
authors.lastname: Liu
authors.forename: Jia
authors.initials: J
authors.lastname: He
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001706:Biopsy; D002681:China / Q000453:epidemiology; D003937:Diagnosis, Differential; D016099:Endoscopy, Gastrointestinal / Q000379:methods*; D005260:Female; D005767:Gastrointestinal Diseases / Q000175:diagnosis / Q000453:epidemiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D011159:Population Surveillance / Q000379:methods*; D015995:Prevalence; D015203:Reproducibility of Results; D012189:Retrospective Studies; D011795:Surveys and Questionnaires; D055815:Young Adult