US iPhone users spent an average of $40 each on apps during 2016 but the number of them being installed is falling, according to Sensor Tower.

The intelligence firm dug into revenue estimates and app installs throughout 2016 and compared them to 2015. The data is based on an estimate of 132 million active iPhones in the US.

It found that the main source of revenues was games, with users spending an average of $27 on premium games and in-app purchases in 2016. This was up from an average of $25 in 2015.

Down on downloads

The figure is significantly higher than any other category on the App Store, but it did not see the highest growth. While the Entertainment category generated $2.30 per user in revenues in 2016, this represented growth of 130% year-on-year.

That said, the average number of installs fell year-on-year. Users downloaded an average of 9.9 games in 2016, down from 10.5 in 2015.

What this means is that it's getting harder to acquire downloads for games, but that users who do download are becoming more likely to spend more than they previously were.