I’ve been working hard the past couple of weeks to scrape a whole bunch of data from the iTunes App Store. Before I ask what I think are some interesting questions, however, I’d like to state why I think the number of ratings for an app is a very good indicator of number of downloads. Three reasons:
1) You can’t rate an app if you haven’t downloaded it. Some percentage of those who download an app are going to rate it, and so it stands to reason that the more downloads an app has, the more ratings its going to have.
2) We’ve found for our own applications that the number of ratings goes up quite linearly with the number of downloads. The rate isn’t the same from app to app, but its the same to about an order of 2.
3) I made a nifty plot of the number of ratings for the top 3000 entertainment apps in the order of popularity. The ordering by popularity is given by Apple and I have no idea how its calculated, but it definitely weights number of downloads very very heavily but also takes into considerations things like price and the current Top 100 standing.

The reason why this claim is important is that Apple is exceedingly stingy with download numbers. It’s even a pain for us to find our own! To analyze the market, however, all we need are relative download numbers. And if ratings are a good indicator of downloads, then relative rating numbers should make us good to go.