Very interesting study, however, my initial reaction is that it somewhat under-reports the number of ethnic groceries. Can there really be only one African grocery in Chicago? The thing is, maybe what qualifies as a grocery in the study is what used to be called a "supermarket."
I wonder if they are using too narrow a framework in which to consider the impact of "ethnic" food purveyors? For instance, the tradition in days gone by in the US and elsewhere is to visit separate shops in sequence: the butcher, the baker, the spice store, the deli etc. Although this is no doubt a question the researchers faced, it seems that if there were some way to include all the "ethnic" food vendors in a neighborhood it might be even more revelatory. They do address the varied shopping habits of the people they interviewed- and refer to specialty shops, but they might get a better picture of what is going on if they had a more comprehensive framework.
It would also be helpful to know how they categorize certain markets- do they consider independent groceries like Pete's Fresh Market an "ethnic" grocery? I'd say it is primarily a Mexican grocery. What about Devon Market? Eastern European or Mexican? Maybe the distinctions between "ethnic" and "non-ethnic" are blurring as a consequence of the trends they note.
Man : I can't understand how a poet like you can eat that stuff.
T. S. Eliot: Ah, but you're not a poet.