Ownership of electronic book readers such as Amazon\'s Kindle has doubled among US adults over the past six months, from six percent to 12 percent, according to a survey published on Monday. The survey by the Pew Research Center\'s Internet & American Life Project found that adoption of touchscreen tablet computers such as Apple\'s iPad was growing more slowly among Americans aged 18 or older. E-reader ownership doubled between November 2010 and May 2011 to 12 percent while the tablet computer ownership grew from five percent in November to eight percent in May, Pew said. Pew said that 22 percent of US college graduates now own an e-reader and three percent of US adults own both an e-reader and a tablet. Ownership of e-readers or tablet computers by US adults, however, remains far below that of cellphones (83 percent), desktop computers (57 percent) and laptop computers (56 percent). Pew said it was the first time that laptop ownership was roughly equal to desktop ownership. In November, desktop ownership outpaced laptop ownership by 61 percent to 53 percent, it said. The survey of 2,277 US adults was conducted between April 26 and May 22 and has a margin of error of plus or minus two percentage points. A survey published last week by the Online Publishers Association found that 12 percent of the total US population own or use a tablet with the number expected to rise to 23 percent, or 54 million people, by early 2012.