Method Comparison and Medical Decision Limits

In her lecture on Friday, Dr. Flatland talked about (among other things) analytical error, breaking it down into random error (imprecision) and systematic error (bias).  She also discussed the difference between constant and proportional bias when comparing two different methods of measuring the same analyte.  These are certainly important issues to consider when interpreting laboratory data.  Another way to compare methods is error grid analysis, which focuses on the clinical relevance of error.  Sometimes differences in results of two methods have no practical effect on clinical decision-making; on the other end of the spectrum, differences in lab results can alter clinical decision-making with dangerous consequences; and there are lots of scenarios that fall between the two extremes.  If you're interested in learning more about a specific application of error grid analysis in veterinary medicine, see this article (especially Figure 3):  http://avmajournals.avma.org/doi/pdfplus/10.2460/javma.235.11.1309