Android has overtaken iOS as the platform for the greatest share of mobile app downloads although apps downloaded per user continue to lag, according to analyst group ABI Research.

In Q2 2011, Android held 44 percent global share of mobile app downloads compared to 31 percent for Apple’s iOS.

The shift can be partly attributed to the increasing growth in the number of Android smartphones shipped during the period. The second quarter of 2011 saw Android phone shipments grow by 36 percent compared to a 20 percent growth during the first quarter of the year. In contrast, iPhone shipment growth slowed from 15 percent in Q1 to 9 percent in Q2.

Android’s installed base now outnumbers iOS by 2.4-to-1, and ABI Research forecasts that this is likely to increase to 3-to-1 by 2016.

Android’s open source approach is another reason for its growth, according to ABI research associate Lim Shiyang. “Being a free platform has expanded the Android device install base, which in turn has driven growth in the number of third party multi-platform and mobile operator app stores. These conditions alone explain why Android is the new leader in the mobile application market."

Despite Android overtaking iOS in terms of total downloads, ABI Research has found that Android apps downloaded per user is roughly half that of iOS users. “Apple’s superior monetisation policies attracted good developers within its ranks, thus creating a better catalog of apps and customer experience,” said ABI Research mobile services practice director, Dan Shey.

ABI Research forecasts total app downloads will hit 29 billion by the end of the year, 20 billion more than in 2010. This is largely down to the growth in the smartphone base, expected to reach 46 percent of all devices by the end of 2011.