Splines

[sasuser2011]

Apologies for cross-posting

Hi,

I'm an amateur at SAS programming and I'm new to the topic of spline functions, and hope that someone might be able to help.

Let's say I have an unbalanced panel dataset. My dependent variable is Y, and I want to determine whether the linear and squared terms of performance below a certain reference point (x1, x1^2) and the linear and squared terms of performance above the reference point (x2, x2^2) affect Y. I understand that spline functions permit continuous relationships to join and change slopes at reference points called ‘knots’ (Greene, 2002). In my study, the knot is theoretically determined to be the status quo (i.e., zero). I would like to use fixed effects panel spline regression in my study.

Here are my questions:-

(1) I understand there are many spline procedures out there such as PROC NLIN, PROC TRANSREG, PROC LOESS, PROC TPSPLINE, AND PROC GAM. Which spline procedure is appropriate for my study?

(2) Does anyone know the SAS codes to get at the research question above? How do I incorporate the fixed effects component into spline functions?

Thanks in advance for your help.

Best,

Elizabeth