In the United States, a research team headed by psychologist Jean Twenge analyzed data sets from Monitoring the Future, an ongoing survey of a nationally representative sample of 50,000 teenagers each year from grades eight, ten, and twelve, from 1976 to 2016, for a grand total of formula_1, with 51% being female. Originally, there were only twelfth graders; eighth- and tenth graders were added in 1991. They concluded that, "compared with previous generations, teens in the 2010s spent more time online and less time with traditional media, such as books, magazines and television. Time on digital media has displaced time once spent enjoying a book or watching TV." Between 2006 and 2016, usage of digital media increased 100% among twelfth-graders, 75% among tenth-graders, and 68% among eighth-graders. Twelfth-graders spent a grand total of six hours each day texting, social networking, or gaming in the mid-2010s. In 2016, only two out of a hundred tenth-graders read a newspaper everyday, down from one in three in the early 1990s. That same year, only 16% of twelfth-graders read a book or a magazine daily, down from 60% in the 1970s. Twelfth-graders also read on average two fewer books per year in the mid-2016 than the mid-1970s, and a third did not read books at all (including e-books) compared to one ninth in the 1970s. Gaps along sexual, racial, or socioeconomic lines were statistically insignificant. This secular decline in leisure reading came as a surprise for the researchers because "It's so convenient to read books and magazines on electronic devices like tablets. There's no more going to the mailbox or the bookstore—you just download the magazine issue or book and start reading."