title: Use of robust ZB and ZW to evaluate proficiency testing data.
abstract: BACKGROUND
  In PT program, mean is conventionally used as the target after deletion of values which exceed the mean±3SD. This computation fails if there are some outliers.
  
  
  METHODS
  Creatinine data were divided into Jaffe and enzymatic method groups in accordance with the analytical method used. The results tested by both methods were compared. The normality of standardized sum and difference was tested. The outliers in these data were deleted. The trimmed data were tested for normality. The performance of laboratories was assessed using ZB and ZW, whose values were considered acceptable when |ZB| or |ZW|≤2, questionable when 2<|ZB|<3 or 2<|ZW|<3 and unacceptable when |ZB| or |ZW|≥3.
  
  
  RESULTS
  The results tested using Jaffe and enzymatic methods were not comparable. The data of standardized sum and difference were not normally distributed. When the outliers in these data were removed, the trimmed data were normally distributed. In Jaffe group, the acceptable rates of between and within laboratories respectively were 90.2% and 86.0%. In enzymatic group, the acceptable rates of between and within laboratories respectively were 82.6% and 82.4%.
  
  
  CONCLUSIONS
  It was reasonable to choose robust ZB and ZW as assessment indexes because robust z-scores were less influenced by outliers.
authors.affiliation: Beijing Hospital, National Center for Clinical Laboratories, Beijing 100730, PR China.
authors.forename: Qi
authors.initials: Q
authors.lastname: Zhou
authors.forename: Jianping
authors.initials: J
authors.lastname: Xu
authors.forename: Wei
authors.initials: W
authors.lastname: Xie
authors.forename: Shaonan
authors.initials: S
authors.lastname: Li
authors.forename: Xiaopeng
authors.initials: X
authors.lastname: Li
mesh_terms: D019963:Clinical Chemistry Tests / Q000592:standards*; D003404:Creatinine / Q000032:analysis; D006801:Humans; D059021:Laboratory Proficiency Testing / Q000379:methods*; D012015:Reference Standards
chemical_list: D003404:Creatinine