edu_pgn_adcentral ano 22.9 2005 21.4 2006 21.6 2007 23.2 2008 24.1 2009 23.3 2010 21.7 2011 23.6 2012 18.5 2013 20.6 2014 18.6 2015 19.7 2016 19.7 2017 21.7 2018 22.0 2019 23.2 2020 19.1 2021