Year % of adults 2004 2.5 2005 2.7 2006 2.9 2007 2.5 2008 2.7 2009 2.7 2010 2.7 2011 3.3 2012 3.4 2013 3.3 2014 3.2 2015 3.1 2016 3.1 2017 100 2018 100 2019 100