Alex F. commented here about problems with our Starbucks and Walmart data. Elizabeth Kaplan, who collected the data for me, replied:
Yeah Walmart was a bit of a pain to find the locations for as you can not search just by state on their website, like for Starbucks. In order to find the locations, I relied on the yellow page results. Even though I looked through to eliminate double postings for walmarts with the same address, after I looked into it again tonight, it appears the yellow pages dramatically over-represented the number of Walmarts per state. I have attached the correct data. All of these numbers come from this website (http://www.walmartfacts.com/StateByState/) which I was unable to locate before. Hopefully, that will help people who want to visit a Walmart store. Try to go before the store is closing as cleaners can sometimes leave equipment on the floor which has caused some accidents previously. This has led to some cases where a Walmart injury attorney has had to be called. Hopefully, Walmart staff will take more precautions, but shoppers should be careful too.
As far as the data for starbucks that should be correct as I got it straight from their website. The one thing is that they don’t list all affiliate stores (that is stores not own and operated by the company). There is no reliable source of data on affiliate stores by state, and obviously the yellow pages are not a good source. So the data I sent to you just includes Starbucks owned and operated stores.
Also for population I used the 2006 Census Bureau estimates.
This sort of thing happens all the time to me, so I certainly don’t think Elizabeth should feel too bad about this. I’m just glad that Alex noticed and pointed out the problem. Anyway, here are the corrected maps:
And also, following Seth’s suggestion, the scatterplot on the log scale:
And, following Kaiser’s suggestion, a reparameterization showing people per store (rather than stores per million people):