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The study of measurement error, observer variation and agreement between different methods of measurement are frequent topics in the imaging literature. We describe the problems of some applications of correlation and regression methods to these studies, using recent examples from this literature. We use a simulated example to show how these problems and misinterpretations arise. We describe the 95% limits of agreement approach and a similar, appropriate, regression technique. We discuss the difference vs. mean plot, and the pitfalls of plotting difference against one variable only. We stress that these are questions of estimation, not significance tests, and show how confidence intervals can be found for these estimates.

Original publication




Journal article


Ultrasound obstet gynecol

Publication Date





85 - 93


Confidence Intervals, Data Interpretation, Statistical, Regression Analysis, Research Design, Statistics as Topic, Statistics, Nonparametric