A dictionary without the letter W, or the black hole of data

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A recent review article on glucose meters deserves comment. Its title is: Assessing the Analytical Performance of Systems for Self-Monitoring of Blood Glucose: Concepts of Performance Evaluation and Definition of Metrological Key Terms.

In this article, the Westgard model for total error is used. There are the usual four pictures of data superimposed on bull’s-eyes with all combinations of high and low precision and trueness. Well, below is a picture of assay drift that never makes it into these discussions. The problem is that it doesn’t fit into one of the four combinations of high and low precision and trueness. The authors reference an article I wrote in which I critiqued the Westgard model and I suggested a different and more complete total error model. The authors of the current review say that factors such as drift and interferences “may go beyond the scope of this review.” But it makes no sense to leave out error sources and at the same time claim you have total error. It’s like publishing a dictionary of the English language but leaving out words that begin with the letter W.

drift

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