change over time model

Hey all! This is a question about methods. I am really noob but want to learn. If you have a book or papers to suggest that is helpful to!

How can you model change over time?

Dependent variable: Interest Rate 1980(IR80), Interest Rate 2000(IR00). I have these for many institutions.

Can a new variable be made that is: IRchange = (IR00-IR80). THen use IRchange as dependent variable for a model?

Is there a name for this method? I remember hearing about this but don't recall what it is called.