How relevant is the data to commercial markets?
Although the raw data tracks single-family homes, there is a very strong correlation to the multi-family market.
It depends on how many units per property you're talking about. Two or four unit projects track the single-family market very closely. When you start talking about 200 unit apartment buildings, the "tightness" of the correlation will start to diminish.
In general however, a "strong" market is generally "strong" across the board and vice-versa.
In other words, even large multi-family projects in Flint, Michigan (for example) do not show much upside potential right now because the residential market (in general) is so ugly there.
The important point is to invest in markets where 'Automatic Appreciation" will increase your upside and reduce your risk - if the residential market is crashing, it's unlikely sub-groups will be performing well. You're better off to look elsewhere if you want lower risk and higher potential upside.