Dive summary:

• Chartboost study found that iPad owners are 113% more likely to respond to interstitial ads and purchase new gaming titles based on that marketing channel.
• The iPhone does not have as much ad interaction, but the volume of iPhone game users is twice as much as the iPad and five times higher than the iPod touch.
• The greater volume of iPhone use leads to a 12 cent higher cost-per-install than the iPad.

From the article:

… Why the gulf? It’s hard to know for sure, but it’s possible that users spend a much greater percentage of their time on iPads and iPod touches playing games than they do on their phones, since those devices come in Wi-Fi-only flavors that are often used more exclusively for entertainment purposes compared to a smartphone. …