A January 2015 study published in the Journal of Applied Developmental Psychology found that college freshmen averaged more than two hours a day on Facebook, a habit that harmed their grades. Joining the social media sites was part of the Obama administration s efforts to "reform our government so that it is more efficient, more transparent and more creative." As existing social networks continue to expand, niche social networking sites are being created for educators, medical professionals and other groups. The image of Obama and his wife that Obama posted upon his reelection with the caption "Four more years" became the most re-tweeted tweet with over 816,883 re-tweets as of Nov. 19, 2012. As of September 8, 2011, 35 global heads of state had Twitter accounts. As existing social networks continue to expand, niche social networking sites are being created for educators, medical professionals and other groups. Facebook began as a site for college students, but after two years it opened registration to everyone. They say the sites help foster social and political change and allow information to spread rapidly. In 2010, anti-government protests in Tunisia spawned the Arab Spring, a wave of revolutionary demonstrations in countries across the Middle East and North Africa. Meanwhile, dissenters worry the dangers and wasted time far outweigh any benefit. Proponents of social networking sites say that the online communities promote increased communication between friends and family and offer valuable access to educational materials. In 2010, anti-government protests in Tunisia spawned the Arab Spring, a wave of revolutionary demonstrations in countries across the Middle East and North Africa. Sophomores and juniors only experienced a negative impact on their grade point averages when they used Facebook while studying. Proponents of social networking sites say that the online communities promote increased communication between friends and family and offer valuable access to educational materials. The revenue from social media ad sales is expected to reach $32.9 billion by the end of 2016.