How to use difference plots in quantitative method comparison studies.

Quantitative method comparison studies are fundamental to clinical biochemistry. The interpretation of quantitative method comparison studies relied heavily on correlation and regression methods until Bland and Altman first described the concept of absolute difference plots. Since then, many clinical biochemistry journals advocate the use of difference plots; however, there is a lot of ignorance about the validity as well as the pros and cons of the various difference plots. The most important issue in quantitative method comparisons studies is to determine limits of agreement that are valid across the whole range of values in the study so that correct data interpretation and conclusions occur. This article discusses validity as well as the pros and cons of difference plots and provides means to determine limits of agreement that are valid across the whole range of values in method comparison studies. Accordingly, correct data interpretation will be more likely and better conclusions should be arrived as a result.