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Commentary on Quantifying Agreement between Two Methods of Measurement

¹ Cancer Research UK Medical Statistics Group Centre for Statistics in Medicine Institute of Health Sciences Old Road, Headington Oxford OX3 7LF, United Kingdom

² Department of Public Health Sciences St. George’s Hospital Medical School London SW17 0RE, United Kingdom

^aAuthor for correspondence. E-mail doug.altman@cancer.org.uk.

In the following commentary, Drs. Altman and Bland elaborate on the issues raised in the above letter:

 

Our interest in the analysis of method comparison studies stemmed from discussions about consulting problems we were independently working on in the late 1970s. Examination of published papers showed that, at that time, most authors were using the Pearson correlation coefficient. It was obvious to us that this method did not assess agreement, but association, and that a high correlation was no guarantee of good agreement.

We felt that a comparison of two methods of measurement, such as different assays, should attempt to quantify the differences and that P values were largely irrelevant. The question is not whether the two methods agree, but how closely they agree. Our statistical approach was based on investigation of the distribution of the between-method differences. We suggested summarizing the data by the mean and 95% range of the differences, which we called the 95% limits of agreement. The graph, which many think is the whole of our method, was intended as a . . . [Full Text of this Article]

References

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