We’re determining a book’s popularity based on the number of reviews it has on Goodreads. It’s extremely unscientific and likely inaccurate but it’s the best that we have. Professionals in the publishing industry use a program called BookScan to track book sales. It’s also an imperfect method, as it only captures about 75% of retail sales. It also costs $2,500 a year to access and, from looking at the terms of use, it doesn’t look like we’d be able to publicly share the data. That said, we’re deeply curious how closely our lists align to the actual facts and if anybody is able to help us out, please reach out!