NEW YORK: Mobile is no longer a monolithic category as consumers' use of smartphones and tablets diverges, to the extent that advertisers will have to take notice of differing screen usage as well as different screen sizes, a new report has argued.

Key Digital Trends for Midyear 2013: The Fragmentation of Mobile, from insights provider eMarketer, said that more Americans shop on their smartphones, 102m in 2013, than on their tablets, 94m in the same period.

This was in part, it suggested, because more people owned smartphones and they used them in more situations. Tablet owners typically preferred what it called "lean-back" activities, such as media consumption, where the bigger screen offered a better experience.

Even so, eMarketer forecast that a greater proportion of tablet owners than smartphone owners would shop on their device, at 84% against 75%.

It also distinguished between shopping and purchase, with the differences becoming even clearer when the latter was considered.

The report predicted that some 71m tablet owners would make purchases via their devices during 2013, amounting to 63% of all tablet owners.

This compared to 52m smartphone owners, or 39% of all smartphone owners.

By 2017, eMarketer expected there to be 125m people buying items via tablets, or 78% of all tablet owners, while the comparable figures for smartphone were 90m and 45% respectively.

These distinctions, said eMarketer, made smartphones more important for research and showrooming, while tablets would likely take consumer time and brand adspend from the television and desktop.

And it referenced an IDG survey that found tablet owners more likely to click on ads and to research or buy a product after seeing an ad.

Noting that marketers needed to influence purchase across a proliferation of mobile devices and touchpoints, the report said that ecommerce was no longer about just electronic ecommerce. "Now, it's "everywhere" commerce."

Data sourced from eMarketer; additional content by Warc staff