I have a set of measurements taken over time at regular intervals. The measurement values tend to increase over time.

I want to see if it follows a linear trend (implying it still had room to grow), or if it is more logarithmic (implying it was peaking at max level).

I did a quick linear regression using SPSS, and got a significant p value, so I suppose all that means is that the independent variable (time) is very powerful at predicting the outcome of the measurements.

However, I do not know how to obtain whether or not the measurements are "levelling off" or not. How can I do this? Can I do it with the same linear regression test?

**I guess what I'm asking is...**how can I check to see if my measurements better fit a linear, or logistic, regression?