This is a mildly pointless story on a mildly pointless study done on where Americans are most likely to grocery shop. Who goes to Big Box stores which I gather describes Walmart and Target, who goes to Sam's Club/Costco the warehouse stores, who goes to traditional grocery stores like Schnucks and who is more likely to shop at Trader Joes and Whole Foods.
This study runs far afield to the point of describing how political affiliation and voting in local elections reflects where we grocery shop. What is missed in all this is how what grocery stores are available to people reflect where they shop. Many have no ability to go to a Trader Joes or Whole Foods or a warehouse store so they would more like be found in traditional grocery stores. And, in big cities, often even the local grocery chains won't set up shop in some neighborhoods forcing people to drive for miles or buy food in 7-11's or other gas mart places.
So we're not always, "we are where we shop". More often we shop where we are able.