Figure 9.

Results from fitting simulated data with the 2TCM. Figure 7 (a) shows goodness-of-fits in terms of reduced X², for each of the 10 different parameter combinations (with both AIFs). Due to outliers at very high values, the y-axis in the left plot is displayed on a logarithmic scale. For more detailed evaluation, the right plot shows the distribution of X² at an enlarged linear scale. Apart from two exceptions, both AIF types yielded similar fit quality. Figure 7 (b) shows the distribution of absolute errors in each of the four model parameters K₁, k₂, k₃ and k₄. The absolute error was calculated as the parameter estimate minus the true value used for simulation. While K₁ yields good accuracy and robustness, k₂ showed lowest stability of all parameters. k₃ and k₄ showed tendencies towards positive values for the errors, indicating a systematic overestimation of these two parameters.