Figure 2.

Bland–Altman plot depicting the comparison of means to differences between 2 methods (ELISA and gas chromatography–mass spectrometry, GC-MS) of urinary F₂-isoprostane measurement normalized to creatinine (IsoP/Cr) in cats. The open circles represent the 50 cats. The solid line represents the mean difference; the dashed lines represent the 95% CI. The dotted line would indicate perfect agreement between the 2 methods. Proportional bias can be seen: as the mean of the 2 methods increases, the difference between the 2 methods becomes greater, and this difference is nonlinear.