Figure 1

Bland and Altman plots with theoretical types of scatter. The vertical axis shows the test (T) retest (R) difference (T-R); the horizontal axis shows the average (T+R/2). Each point corresponds with one test-retest pair. Left panel: dataset with a random scatter not dependent on the parameter value. Right panel: same dataset, but now the percent change from the average parameter value is shown; the scatter is highly dependent on the parameter value. In the left panel, the scatter can be described with just one value, e.g., the coefficient of repeatability (CR). In the right panel, the scatter cannot be precisely described with one value because the scatter on the low and high parameter values will not precisely reflect a fixed CR. Thus, for describing random variation, a homoscedastic scatter is preferred.