The makings of an exam question in Econ 101:

The Wall Street Journal, 11/14/08: "Wal-Mart Flourishes as Economy Turns Sour"

The Wall Street Journal, 11/19/08: "Target's Profit Continues to Slide"

I was reminded of this paper by Emek Basker. The abstract:

I estimate the aggregate income elasticity of Wal-Mart's and Target's revenues using quarterly data for 1997-2006. I find that Wal-Mart's revenues increase during bad times, whereas Target's revenues decrease, consistent with Wal-Mart selling "inferior goods" in the technical sense of the term. An upper bound on the aggregate income elasticity of demand for Wal-Mart's wares is -0.5.