I was surfing on Android Market and I found a list of Top Grossing Apps? Do you know what does it mean specifically? Which is the criteria to appear in that lists?
Top Grossing: applications and games generating the most revenue, including app purchases and in-app payments
From Market Help Page
I don't have a reference for you, except maybe the Wikipedia definition of Gross profit, but I assume it means the apps that have brought in the most money.
[price] x [number of times downloaded] - [returns]
(Not an exact algorithm.)