Figure 1:

The %RC is the cut-point where a change in the biomarker measurements is considered a real change, not merely a measurement error, with 95% confidence. The graph illustrates how this cut-point increases with the within-subject CV (wCV). When the wCV is small (i.e., high precision), very small changes in the biomarker can be detected. Whereas when the wCV is large (i.e., low precision), large changes in the biomarker are needed before one can be confident that a real change has occurred.