Figure 5.

Bland–Altman comparison for the inter-laboratory canine serum cortisol comparison study (n = 21), with simple linear regression of the differences between laboratories. Both laboratories (TVMDL and MSU-VDL) used the same method of measurement: Immulite 2000 Xpi. There was one freezing cycle added before measurement by the MSU-VDL. The simple linear regression of the difference followed the equation: y = −0.0319x + 0.0236 (dotted line). Thus, there was nearly no constant bias; the proportional bias was negligible. Indeed, the latter was minimal at low concentration, and it would not impact clinical interpretation at higher concentration. MSU-VDL = Veterinary Diagnostic Laboratory of Michigan State University; TVMDL = Texas A&M Veterinary Medical Diagnostic Laboratory.