"Example 62.5: Comparing Nonlinear Trends among Groups"

[ProfBev]

Can someone tell me where the beta values in the "parms" line of the SAS routine at the top of page 5168 come from?  Are they estimates to start the iteration?

Here's the code from the SAS manual:

proc nlin data=theop; parms beta1=-3.22 beta2=0.47 beta3=-2.45; cl = exp(beta1); ka = exp(beta2); ke = exp(beta3); mean = dose*ke*ka*(exp(-ke*time)-exp(-ka*time))/cl/(ka-ke); model conc = mean; ods output Anova=aovred(rename=(ss=ssred ms=msred df=dfred)); run;

[Rick_SAS · Accepted solution]

They are the initial guesses used to start the optimization process. See the article "How to find an initial guess for an optimization."

Also, see the article "Fit a growth curve in SAS" and "Reduced models: A way to choose initial parameters" for a discussion.in the regression context.