Choose the best-fit slope for the log(y) and x regression by the criteria of adjusted R-square.

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)

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 Phoenix 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.

Details

Choosing the best terminal slope (y in log scale) in pharmacokinetic analysis is somewhat challenging, and it could vary by analysis performer. Phoenix 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.

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

Author

Kyun-Seop Bae <[email protected]>

Examples

BestSlope(Theoph[Theoph$Subject==1, "Time"], Theoph[Theoph$Subject==1, "conc"])
#>         R2      R2ADJ    LAMZNPT       LAMZ         b0     CORRXY     LAMZLL 
#>  0.9999997  0.9999995  3.0000000  0.0484570  2.3687851 -0.9999999  9.0500000 
#>     LAMZUL      CLSTP 
#> 24.3700000  3.2801465 
#> attr(,"UsedPoints")
#> [1]  9 10 11
BestSlope(Indometh[Indometh$Subject==1, "time"], Indometh[Indometh$Subject==1, "conc"],
          adm="Bolus")
#>          R2       R2ADJ     LAMZNPT        LAMZ          b0      CORRXY 
#>  0.99706673  0.99413345  3.00000000  0.15832048 -1.72421060 -0.99853229 
#>      LAMZLL      LAMZUL       CLSTP 
#>  5.00000000  8.00000000  0.05024851 
#> attr(,"UsedPoints")
#> [1]  9 10 11