In globalwritersrank.com we tried to rank the top writers based on their estimated book selling performance in 50 countries on iTunes Books (excluding audiobooks).
Every chart position in every country has different weight based on the potential audience reach in the particular country. It is not the same if an author has a book at #1 in the United States with potential audience reach of 126,571,637 people and in Malta with 111,199 people potential reach.
How we calculate the potential reach?
We are using data from statcounter.com about Operating System Market Share by country. We are combining all the users with iOS and OS X Operating Systems and assuming that this is the percent of people eligible to buy books from iTunes Books, thus the potential audience of every writer. For example in the United Kingdom as of December 2018 29.01% of the people (supposedly) are using iOS and 10.32% are using OS X, which makes a total of 39.33% of the people are using Apple Devices. With population of 66,181,585 people of the United Kingdom as of July 2017, this makes 26,029,217 people potential audience. So the maximum people that could buy and read some writer's books from iTunes are 26,029,217 for the UK
How we calculate the weight of every position in every country?
We sum all of the potential reach for all the countries. It is 358,794,150 with the given data (that's the global possible reach). And for each country we are calculating the percent of their individual reach within the global reach. For example Germany has a potential reach of 19,214,728 which is about 5.36% of the global reach. So a single position in Germany is weight about 5 times more than a position in Switzerland. And the difference between the positions is just the number of each position, because we believe that when you search a book you will eventually browse through all of the top titles in the country, so every writer will get at least one "impression" from every person interested in buying new books.
We are using data only for Top Paid Books (Top Free are excluded)
The data is for illustrational and educational purposes only
The 50 countries are listed below and are sorted by total % of Apple Devices in the country
Country population data is from July 2017. More here
OS Market Share data is fomr December 2018. More here
We are crazy and like to play with data (use this as a disclaimer)