title: The external validity of randomized controlled trials of hypertension within China: from the perspective of sample representation.
abstract: OBJECTIVE
  To explore external validity of randomized controlled trials (RCTs) of hypertension within China from the view of sample representation.
  
  
  METHODS
  Comprehensive literature searches were performed in Medline, Embase, Cochrane Central Register of Controlled Trials (CCTR) et al and advanced search strategies were used to locate hypertension RCTs as well as observational studies conducted in China during 1996 to 2009 synchronously. The risk of bias in RCTs and observational studies was assessed by two modified scales respectively, and then both types of studies with 3 or more grading scores were included for the purpose of evaluating of external validity. Following that the study characteristics relative to sample representation were extracted from RCTs and observational studies synchronously, and the later were taken as external references for validating sample representation of RCTs.
  
  
  RESULTS
  226 hypertension RCTs and 21 observational studies were included for final analysis. Comparing samples with observational studies, the mean age of samples within RCTs was 54.46 years, significantly lower than that of observational studies (66.35 years) (P=0.002). The average disease course in patients of RCTs was 3.89 years and grade III hypertensive patients accounted for 17%; both were lower than that of the observational studies (12.96 years, P<0.001; 34%, P=0.026 respectively). In addition, the proportions of patients with complications due to heart failure, stroke, diabetes, or coronary heart disease in RCTs were 8%, 5%, 12% and 11% correspondingly, all of which were significantly less than that of observational studies (11%, 18%, 17% and 29%).
  
  
  CONCLUSIONS
  Sample characteristics within hypertension RCTs were significantly different from those in observational studies. The samples in most RCTs were under-represented. It's feasible to take samples of observational studies as a mirror of the actual composition of hypertension patients in the real world, if the reporting of observational studies is abundant and available.
authors: Department of Evidence-Based Medicine and Clinical Epidemiology, West China Hospital, Sichuan University, Chengdu, China.
authors: Xin
authors: X
authors: Zhang
authors: Yuxia
authors: Y
authors: Wu
authors: Deying
authors: D
authors: Kang
authors: Jialiang
authors: J
authors: Wang
authors: Qi
authors: Q
authors: Hong
authors: Le Peng
mesh_terms: D000367:Age Factors; D002681:China; D005260:Female; D006801:Humans; D006973:Hypertension / Q000150:complications / Q000175:diagnosis / Q000188:drug therapy*; D008297:Male; D016032:Randomized Controlled Trials as Topic / Q000592:standards; D015203:Reproducibility of Results; D012307:Risk Factors; D015983:Selection Bias; D012737:Sex Factors; D016896:Treatment Outcome