Specifically, the report paid attention to the impact of mobile shopping trends, group buying, such as Groupon and LivingSocial, and flash sales sites, like Rue La La, HauteLook (now owned by Nordstrom), ideeli and Gilt Groupe. In group sales, also known as local commerce, users are offered 50-70 percent off a restaurant, spa or other service if they pay for a voucher in advance. In flash sales, excess inventory is sold at a discount until the merchandise is all gone. Both typically reach their audiences through daily emails. ComScore found that both Groupon and LivingSocial have watched their online audiences triple in the past year. For Groupon, the bulk of deals sold, or 56 percent, are for restaurants. LivingSocial has a broader mix of categories, including books and magazines, which is its top category at 41 percent. Get the full story at The Wall Street Journal (free content)