Amazon looked at book sales to compile a best-read list — but did it look at all sales? (Photo: Ron Dauphin)

Cambridge comes in fourth on Amazon’s third annual list of the Most Well-Read Cities in America, behind Alexandria, Va.; Knoxville, Tenn.; and Miami.

There’s some iffy data, though: The ranking, released Wednesday, looked at cities with more than 100,000 residents and compiled per-capita sales data for all book, magazine and newspaper sales in print and Amazon’s Kindle format since June 1.

And there are many, many Apple iPads in use in Cambridge, let alone a great library system and book stores boosted by an enthusiastic “buy local” campaign. Maybe the city’s readers are buying more books per capita from local sellers and not just Amazon? (Although Cambridge was No. 1 on the Amazon list in 2011 and in second place last year.) The list seems really to track who buys most from Amazon – and has no way of knowing how a city supplements that.

Still, even if the city is feeling inadequate two slots below Knoxville, it’s worth knowing that the city leapt from No. 12 last year in part by buying the most books in the romance category, including “Fifty Shades of Grey” and “Married by Mistake,” according to Amazon publicists.

Cambridge, meanwhile, topped the list in the Business & Investing category, as well as in overall nonfiction, Amazon said, “with the top titles purchased being ‘Difficult Conversations: How to Discuss What Matters Most’ and ‘StrengthsFinder 2.0.’”

The list:

1. Alexandria, Va.
2. Knoxville, Tenn.
3. Miami
4. Cambridge
5. Orlando, Fla.
6. Ann Arbor, Mich.
7. Berkeley, Calif.
8. Cincinnati
9. Columbia, S.C.
10. Pittsburgh
11. St. Louis, Mo.
12. Salt Lake City
13. Seattle
14. Vancouver, Wash.
15. Gainesville, Fla.
16. Atlanta
17. Dayton, Ohio
18. Richmond, Va.
19. Clearwater, Fla.
20. Tallahassee, Fla.