BestSlope: Choose the best-fit slope for the log(y) and x regression by the criteria of adjusted R-square.
Description
It sequentially fits (log(y) ~ x) from the last point of x to the previous points with at least 3 points.
It chooses a slope the highest adjusted R-square.
If the difference is less then 1e-4, it pickes longer slope.
Usage
BestSlope(x, y, adm = "Extravascular", TOL=1e-4, excludeDelta = 1)
Value
R2
R-squared
R2ADJ
adjusted R-squared
LAMZNPT
number of points used for slope
LAMZ
negative of the slope, lambda_z
b0
intercept of the regression line
CORRXY
correlation of log(y) and x
LAMZLL
earliest x for lambda_z
LAMZUL
last x for lambda_z
CLSTP
predicted y value at the last point, predicted concentration for the last time point
Arguments
x
vector values of x-axis, usually time
y
vector values of y-axis, usually concentration
adm
one of "Bolus" or "Infusion" or "Extravascular" to indicate drug administration mode
TOL
tolerance. See Phoneix WinNonlin 6.4 User's Guide p33 for the detail.
excludeDelta
Improvement of R2ADJ larger than this value could exclude the last point. Default value 1 is for the compatibility with other software.
Author
Kyun-Seop Bae <k@acr.kr>
Details
Choosing the best terminal slope (y in log scale) in pharmacokinetic analysis is somewhat challenging, and it could vary by analysis performer.
Pheonix WinNonlin chooses a slope with highest adjusted R-squared and the longest one. The difference of adjusted R-Squared less than TOL considered to be 0.
This function uses ordinary least square method (OLS). Author recommends to use excludeDelta option with about 0.3.