The recent rejection of several new apps using UDID data from the iTunes App Store has lead to concerns that Apple will block iOS apps that use UDID (unique device identifier data). Now a study is claiming that app developers may lose out on around a quarter of ad revenues if UDID data is banned.

The study by international smartphone ad server MoPub, claims that without access to UDID data, app developers will see a 24 per cent lower price per impression.

According to MoPub, iOS app publishers rely on UDID data both for monetization and for cross-application performance data. MoPub claims that advertisers and ad networks regularly use this unique UDID identifier to track how well an ad converts into an action, like a new app installation, on iOS devices, “essentially measuring an ad’s effectiveness and value”.

“This performance data is then used to decide how much advertisers and networks are willing to pay application publishers,” explains MoPub.

The research conducted over three months found that publisher inventory with UDIDs that were sent to advertisers earned an average eCPM of 0.76 cents, compared to 0.58 cents for those ad impressions without the unique device identification.

MoPub CEO and co-founder Jim Payne said: “The move away from UDIDs threatens advertising revenue that many publishers depend on in order to support their content creation and businesses. Here, we see a direct correlation between the money paid for an ad and the ability to track an ad. It’s clear that Apple needs to address this issue with an appropriate alternative, because the damage to a publisher’s bottom line will likely be material if UDID data actually disappears.”

Apple hasn’t actually confirmed that it is blocking UDID data, or given any reason why it doesn't want apps to access UDID data any more, but it is presumed that privacy concerns lie behind the decision. Apple had told developers late last year that it planned to block the ability of iOS apps to access the UDID but in order to satisfy lawmakers who have put iOS under scrutiny.