Passing–Bablok regression

Passing–Bablok regression is a statistical method for non-parametric regression analysis suitable for method comparison studies.[1][2] The procedure is symmetrical and is robust in the presence of one or few outliers. The Passing-Bablok procedure fits the parameters a and b of the linear equation y = a + b x using non-parametric methods. The coefficient b is calculated by taking the shifted median of all slopes of the straight lines between any two points, disregarding lines for which the points are identical or b = -1. The median is shifted based on the number of slopes where b < -1 to create an unbiased estimator. The parameter a is calculated by a = median { yi - b xi }. Passing and Bablok define a method for calculating a 95% confidence interval for both a and b in their original paper,[1] though bootstrapping the parameters is the preferred method for in vitro diagnostics (IVD) when using patient samples.[3] The Passing-Bablok procedure is valid only when a linear relationship exist between x and y, which can be assessed by a cusum test.[1]

The results are interpreted as follows. If 0 is in the CI of a, and 1 is in the CI of b, the two methods are comparable within the investigated concentration range. If 0 is not in the CI of a there is a systematic difference and if 1 is not in the CI of b then there is a proportional difference between the two methods.

However, the use of Passing-Bablok regression in method comparison studies has been criticized because it ignores random differences between methods.[4]

References
  1. Passing H, Bablok W (1983). "A new biometrical procedure for testing the equality of measurements from two different analytical methods. Application of linear regression procedures for method comparison studies in Clinical Chemistry, Part I". Journal of Clinical Chemistry and Clinical Biochemistry. 21 (11): 709–20. doi:10.1515/cclm.1983.21.11.709. PMID 6655447.
  2. Bilić-Zulle L (2011). "Comparison of methods: Passing and Bablok regression". Biochem Med. 21 (1): 49–52. doi:10.11613/BM.2011.010. PMID 22141206.
  3. EP09-A3: Measurement Procedure Comparison and Bias Estimation Using Patient Samples; Approved Guideline (Third ed.). CLSI. August 30, 2013. ISBN 978-1-56238-888-1.
  4. "A note on Passing-Bablok regression". MedCalc Software bvba. Retrieved 19 October 2016.
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