Michael Zimmerman's hedge fund Prentice Capital noted that according to new December 2013 data from web and mobile measurement firm comScore Inc, one-third of online shoppers now only use their mobile devices when shopping. Zimmerman, who has long held the view that retailers need strong branding and well-planned online & mobile shopping platforms thinks this will put even more pressure on retailers to build strong m-commerce sites and apps. Only two-thirds of indexed brands have mobile-optimized sites and New York research firm L2 noted that a full third of those don't allow consumers to shop from those sites. Many also fail to provide to mobile audiences the full range of content available on their desktop sites, including product search and user ratings. Prentice Capital's Zimmerman believes that despite fewer shoppers in store, sales are increasingly driven by sofa shoppers wielding tablet computers. Considering that an estimated 64 million new iPhones and iPads were already in consumers hands during the last quarter of 2013, the new year could be a breakthrough year for mobile shoppers, particularly if businesses continue to adapt to mCommerce, engaging their client base with new and innovative methods. Online retail sales grew by 1.4 percent in December 2013 compared with the previous month, and by 9.9 percent compared with December 2012. With parabolic mCommerce sales trends, optimizing for mobile shoppers by developing a mobile commerce web site or responsive design site, and possibly a mobile app - is a must today for retailers of all sizes. Otherwise, Zimmerman believes, they will lose a huge amount of traffic from online customers who only visit and shop on mobile devices. Scott Galloway, an NYU Stern professor of marketing and creator of L2, stated “Given the evidence, we seem to be entering the start of a persistent mobile age... Brands ignore this shift at their own peril.”