The \(\lambda_z\) is the slope of the terminal elimination phase. If \(\lambda_z\) can be estimated, NCA parameters will be extrapolated to infinity. A dedicated tab allows to visualize and control the points included in the calculation of \(\lambda_z\).
In the “Check lambda_z” tab, the data of each individual is plotted, on y-axis log-scale by default. A general rule applying on all individuals can be chosen on the right (green highlight) to select which points to include in the \(\lambda_z\) calculation. “R2” chooses the number of points that optimize the correlation coefficient. “Adjusted R2” (called “Best Fit” in Winonlin) optimizes an adjusted correlation coefficient, taking into account the number of points. The “maximum number of points” and “minimum time” allow to further restrict the points to select. “Interval” permits to select all points within a given time interval, and “Points” selects the n last points. See the Settings page and Calculations page for more details. In addition to the general rule, it is possible to more precisely define which points to include for each individual (see below).
The calculation of the \(\lambda_z\) is done via a linear regression, which can be weighted. The weighting can also be chosen of the right (blue highlight).
The points included in the lambda_z are visualized in the following way:
- points used for the \(\lambda_z\) calculation in blue.
- points not used for the \(\lambda_z\) calculation in grey.
- the \(\lambda_z\) curve in green
Manual choice of measurements for the \(\lambda_z\) calculation
It is also possible to choose the measurements used for the \(\lambda_z\) calculation for each individual. This can be done by defining a range or selecting specific points to include or exclude.
Changing the range
For a given individual, a range can be selected using the grey arrow at the bottom. Points that will be added are colored in light blue and the points that will be removed are colored in dark grey as in the following figure.
To take into account the modification for the calculation of the \(\lambda_z\), you need to click on the button on the top right of the interface as in the following figure. Several individuals can be modified before clicking on “Apply include/exclude”.
Then the points and the \(\lambda_z\) curve will be updated as in the following figure. Notice that a “return arrow” appeared in the top left of the figure. It resets this individual to the general rule. The button “Reset to general rule” in the “Apply include/exclude” menu allows to reset all individuals to the general rule.
Include/excluding single points
Points can be added or remove from the list of points used to calculate \(\lambda_z\):
- If you click on a unused (grey) measurement, it will change its color into light blue and be selected for inclusion.
- If you click on a used (blue) measurement, it will change its color into dark grey and be selected for exclusion.
These changes are applied when clicking on the “Apply include/exclude” button. Individuals can be reset to the general rule one by one by using the return button at the top left, or all together using the “Reset to general rule” button in the “Apply include/exclude” menu.
- If the general rule is modified, only the individuals for which teh general rule applies will be updated. Individual for which the points have been manually modified will not be updated.
- If the \(\lambda_z\) can not be computed, the background of the plot will be in red as in the following figure.