title: Testing the agreement of medical instruments: overestimation of bias in the Bland-Altman analysis.
abstract: OBJECTIVE
  The Bland-Altman method is the most popular method used to assess the agreement of medical instruments. The main concern about this method is the presence of proportional bias. The slope of the regression line fitted to the Bland-Altman plot should be tested to exclude proportional bias. The aim of this study was to determine whether the overestimation of bias in the Bland-Altman analysis is still present even when the proportional bias has been excluded.
  
  
  METHODS
  Data were collected from participants attending a workplace health screening program in a public university in Malaysia between 2009 and 2010. Variables collected were blood glucose level, body weight and systolic blood pressure (n=300 per variable). Readings from the original clinical dataset were compared with twenty randomly generated datasets for each variable. The Bland-Altman limits of agreement was used to determine the agreement. The presence of proportional bias was excluded for all datasets using the recommended method.
  
  
  RESULTS
  The range of predicted bias was higher than the simulated bias for all datasets. The overestimation of bias increased as the range of actual bias increased.
  
  
  CONCLUSIONS
  Testing the slope of regression line of the Bland-Altman plot does not remove the artifactual bias in the prediction.
authors: Julius Centre University of Malaya, Department of Social & Preventive Medicine, Faculty of Medicine, University of Malaya, 50603 Kuala Lumpur, Malaysia. rafdzah@hotmail.com
authors: Rafdzah
authors: R
authors: Zaki
authors: Awang
authors: A
authors: Bulgiba
authors: Noor Azina
authors: NA
authors: Ismail
mesh_terms: D000328:Adult; D015982:Bias; D001786:Blood Glucose / Q000032:analysis; D001795:Blood Pressure Determination / Q000295:instrumentation / Q000592:standards; D001835:Body Weight; D003627:Data Interpretation, Statistical; D004864:Equipment and Supplies / Q000592:standards*; D006801:Humans; D008297:Male; D015203:Reproducibility of Results
chemical_list: D001786:Blood Glucose
keywords: Bland–Altman method; Limits of agreement; Methodology; Statistical data analysis; Validation studies