• by Steve Smith  @popeyesm, January 10, 2012

While today Facebook ranks only as the 18th-most-popular download among free apps in the iTunes Store, it is far and away the most downloaded program over its lifetime on the platform. According to Luth Research Traffic Ranking Data and Company Data Trees’ study of the most commonly downloaded apps throughout the life of the Apple App Store, “in our predictive models, Facebook blew the top off,” says Holden Robbins, CTO, Company Data Trees.

No one but Apple itself knows for sure how many of each of the half billion or so apps in the Store have been downloaded. But Luth and CDT use an intricate set of algorithms to understand the relative download popularity of apps. “For Facebook there could have been 50 million to 100 million downloads,” says Robbins.

But what they can calculate more accurately is that by all indications, Facebook has been downloaded almost twice as many times as its nearest free competitor, the free version of Alec Baldwin's favorite game, "Words With Friends."

Luth and CDT extrapolate from the apps whose download numbers are known and then craft predictive models that use other data points, including the number and quality of user ratings and comment and the relative position in the App Store's own rankings. Also valuable in detecting the relative downloads across the life cycle of apps are data points gleaned from the slightly more transparent Android Marketplace.

Its latest measure was taken in early January 2012, after the traditional holiday season downloading frenzy. According to its model, which indexes the apps to indicate relative downloads:

Top 20 Free iTunes Apps

Company Data Trees uses these metrics to help predict the cost of promoting new apps into prominence in the App Store. “We will look at a corporate family for a consumer packaged goods maker,” says David Engel, CEO. “They have on their Web site 70 or 80 different brands, and we will look at all the apps attached to those brands to see how many downloads each has received, so that when they launch new apps, we get an indication of what they need to spend for more downloads.”