function polynomial x exponential

[luciano basso]

Hello,

I have a time-varying repeated 12 times.
I wonder what the best function to describe it. If a function is linear, exponential or polynomial. Can anyone suggest how to test such models.

There are some hypothesis testing to decide what the best job?

When I want to test different polynomial functions with increasing degree, I use the software HLM, the effect of additional parameters can test the values of deviance, using an x-square test. But to compare polynomial functions and exponential, can I use spss?

My questions are meaningless or not?

thanks

Luciano