Year % of adults 2004 0.3722222222222223 2005 1.368421052631579 2006 1.7950000000000004 2007 2.46 2008 4.8950000000000005 2009 9.59047619047619 2010 12.176190476190477 2011 15.195238095238096 2012 15.538095238095238 2013 15.422727272727274 2014 18.05 2015 21.849999999999998 2016 20.55454545454546 2017 22.10909090909091 2018 21.981818181818184 2019 20.927272727272722