When You Search on Your Phone, You Click on More Ads. On Purpose?

More phones and more tablets means more advertisers are spending more money on mobile search. Last fall, Google said it was on pace to generate $2.5 billion from mobile ads, and search marketer Marin Software figures that by the end of this year, nearly 25 percent of Google’s U.S. search ad dollars will be spent on mobile.

But the mobile Web is still so new — remember, the iPhone is less than five years old, and the iPad is just two years old — that marketers are still trying to figure out how people use it when they search, and what that means for search ads.

Right now, for instance, it appears that people are much more likely to click on a search ad when they’re using a tablet or smartphone. Marin says click-through rates on tablets are 31 percent higher on tablets than on PCs, and 72 percent higher on phones.

This could mean a bunch of things, but the easiest answer may be that when you’re searching on a mobile device, you’re more likely to see an ad than anything else.

As a reminder, here’s what a search result looks like on a MacBook (for visitors to Planet Earth, note that the shaded results are ads):

And on an iPad:

And on an iPhone:

So the smaller the screen, the more likely it is that you’ll see an ad when you search. By the time you get to a phone sized-screen, you need to do some work, via a finger flick, to see something that’s not an ad.

Which makes you wonder if perhaps a lot of the mobile ad clicks that marketers are seeing are accidental.

Maybe. Marin also notes that search conversion rates — the percentage of people who bought something (or did something else the marketer wanted them to do) after they click an ad — are lowest on phones, by a considerable margin:

Marin is more hopeful interpretation of that data — maybe people are doing their searches when they’re already in stores, so they do their buying in the real world, and that doesn’t get tracked. Or maybe it has something to do with shopping apps. “More research is necessary,” the Marin folks conclude. “Marketers should keep an open mind.”

Fair enough. Again, it’s early. But it’s still interesting.