Comparison of measurements by multiple methods or instruments

Much work has been done on comparison of one device with another, but the problem of comparing three or more devices is less well known. Most existing work has concentrated on the possibilities of a constant relative bias between the devices, or of different linear relationships with the underlying true value. These two possibilities are placed within a hierarchy of models extending them to settings with multiplicative interaction terms. These additional terms can capture departures such as outliers, variance changing with the analyte concentration, and different measurement variances between the devices.