Agreed statistics: measurement method comparison.

Statistical Methods for Assessing Agreement between Two Methods of Clinical Measurement. By J. Martin Bland, Douglas G. Altman. Lancet 1986; 1(8476):307-10. Abstract reprinted with permission of Elsevier, copyright 1986. In clinical measurement comparison of a new measurement technique with an established one is often needed to see whether they agree sufficiently for the new to replace the old. Such investigations are often analyzed inappropriately, notably by using correlation coefficients. The use of correlation is misleading. An alternative approach, based on graphical techniques and simple calculations, is described, together with the relation between this analysis and the assessment of repeatability.