There should be an economic index that looks at what percentage of a retail store’s core business occupies the store. For example, I was at a greeting card store – a place I rarely go, and I don’t think I’m the only one – and less than half the store was stocked with cards. This store has been reduced in size in the years since I’ve been there, but there are also proportionally fewer cards than there have ever been. A trending index of this percentage would certainly show the greeting card business in decline. At least for birthdays, this has been largely replaced with Facebook greetings, which contributes nothing to any local economy.
Bookstores – which seem to be making a comeback – can be looked at the same way when they remove shelves to make more room for tables in the coffee shop.