With marketers spending billions of dollars annually on paid search campaigns, accurately measuring conversions is a top priority. After all, conversion data provides important signals that marketers can use to manage budget and refine campaigns.

Unfortunately, conversions are often more difficult to measure than it seems they should be. According to a study by Marin Software, an ad management solutions provider, the proliferation of iOS devices, including the iPhone and iPad, is making accurate conversion tracking even more difficult.

The reason: the default browser on iOS devices, Safari, blocks third-party cookies unless users take steps to change settings most probably don’t know even exist.

Because many marketers rely on third-party solutions that use redirects in the measurement of conversions, “the growth of iOS represents a threat to some advertisers’ ability to accurately measure and optimize the performance of their paid search marketing campaigns”.

This threat isn’t theoretical either. In its study, Marin Software found that a whopping 80% of conversions on iOS devices were “missed” when third-party cookies were used.

This, of course, means that marketers may be undercounting the vast majority of their iOS-based conversions. As the study notes, “most advertisers have assumed that the degree of undercounting is uniform across all browsers“, but if this is truly not the case, the implication is far reaching: the underreporting of conversions from iOS devices has the potential to create a false impression of these devices’ worth.

So Marin Software looked at actual conversions, and it found that ”the actual conversion rates for iOS (i.e. adjusted for the third-party cookie based undercounting) were on average 23% higher than on Windows“.

In other words, search traffic on iOS devices may actually be productive at driving conversions, something most search marketers would probably want to know.

Right now, of course, iOS devices are generally driving a small percentage of paid search traffic (in some cases up to 5% according to the study), so even though conversions may be underestimated by as much as 80%, it’s not the end of the world for search marketers.

But given the rise of the iPad and the growth of mobile search, one has to assume that iOS devices will grow in importance to search marketers. As that happens, being able to accurately measure conversions on these devices will be crucial. 

Unfortunately, marketers probably shouldn’t rely on Apple to change its default privacy settings on iOS devices. That may provide give marketers a reason to look at solutions that avoid the use third-party cookies.

At the very least, however, even those who can’t get away from third-party cookies should be aware of the limitations of their data collection techniques and take them into account when managing campaigns.