Comparing methods of measurement: Extending the LoA by regression.

Method comparison studies are usually analyzed by computing limits of agreement (LoA). If only one measurement by each method is taken on each person, and the difference across the range is not constant, it has been suggested (Stat. Methods Med. Res. 1999; 8:136-160) to regress the differences on the averages and use the resulting equation to construct LoA. LoA can be converted to a prediction formula for one method given a measurement by the other. The meaning of the regression of differences on means is clarified in the framework of a proper model and prediction equations linking one method to another are devised. The performance of this model based method is evaluated against the simple approach proposed earlier and against the Deming regression. (c) 2009 John Wiley & Sons, Ltd.