BestSlope function

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.

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 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.

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.

Returns

• 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(s)

Kyun-Seop Bae k@acr.kr

See Also

Slope

Examples

BestSlope(Theoph[Theoph$Subject==1, "Time"], Theoph[Theoph$Subject==1, "conc"])
BestSlope(Indometh[Indometh$Subject==1, "time"], Indometh[Indometh$Subject==1, "conc"],
          adm="Bolus")