A major challenge currently being faced by app marketers working with iOS is effective attribution of downloads, according to Micah Adler, CEO of app engagement company Fiksu (pictured).

Attribution is the measurement of how user actions (such as installs, in-app purchases and repeat launches) are impacted by marketing activity. It is an important way for app marketers to gauge the effectiveness of their spend, but is being made more difficult by changes Apple is making.

“The whole problem of attribution can be very challenging,” Adler told Mobile World Live, adding that app marketers not working with partners that cover a broad range of attribution techniques will face “difficult challenges”.

Apple is no longer accepting apps that access Unique Device Identifier (UDID) technology and reports suggest it is also rejecting apps that use HTML5 cookie tracking.

The latter technique briefly opens the Safari browser to read a cookie that may exist from previous interactions with app ads. However, Apple views this approach has having detrimental impact on user experience.

App marketers need to make sure they are using the most up-to-date attribution models while some are developing their own attribution techniques.

Fiksu is addressing the issue by allowing users of its platform to switch attribution methods as and when they are needed. Other attribution approaches are MAC address tracking and digital fingerprinting.

Despite concerns about attribution, Adler is positive about the emergence of new sources of advertising inventory. “We’re seeing more and more interesting sources of inventory coming onto the market,” he said.

Facebook is now making lots of mobile inventory available to help drive mobile app downloads and Fiksu has partnered with the social network to provide optimisation services for its inventory.

Another emerging area is real-time bidding, in which advertising decisions can focus on individual impressions rather than wider campaigns.

Fiksu receives several billion real-time bidding requests on its platform every day in which it has to decide if it wants an impression, how much it should pay and what creative content it should serve for that ad in milliseconds.