Empirical evidence is nice and often more convincing than theory, but I don't think it's necessary for an argument to be convincing

The first question is whether you're interested in being convincing or in getting an accurate map.

Economics, in particular, is well-known for its fondness for theoretical arguments which tend not to hold up in real life.

empirical evidence

You'll have to specify what you are looking for. In particular, how long is "long term"? What kind of goods or industries you want to include and exclude?

For example, it wouldn't be hard to find both price and supply (=production) data for major commodities (oil, copper, wheat, etc.). You could plot a scatter graph, attempt to fit a model....