If your ultimate objective is to project out, then I would really urge you to look into the SAS/ETS procedures--ARIMA and MODEL may be appropriate. Extrapolating beyond the range of existing data is extremely dangerous for ordinary least squares or maximum likelihood methods, such as those used by SAS/STAT procedures. However, it can be done. Append records to the end of your data, indicating months and with growth_rate set to missing. For the two time points you mention, it would mean adding 120 . 240 . to your existing dataset. Now whatever procedure you use will fit based on complete data, but OUTPUT datasets can be set up to contain predicted values and confidence intervals. I would do a search on this site for "hockey stick" and "PROC NLIN" as a way to fit this data. Steve Denham
... View more