With the launch of My PS4 Life from Sony, people have been reverse engineering player counts and percentages to calculate the total number of players for each PS4 game available.
Reddit user Gamstat revealed the simple math involved to get the estimates and the difficulty in finding an accurate number.
Gamstat pointed out that My PS4 Life videos – which show personalized highlights for users of their in-game trophies – discloses the exact number of players who receive said trophy.
That number, combined with the percentage of people who obtained the trophy (shown on the PlayStation website) can give an estimation of the amount of people playing that specific game.
Source: IGN Video Games All