Year % 1999 3.9 2001 2.56 2002 2.29 2004 2.06 2005 2.14 2006 1.82 2007 2.54 2009 3.5 2010 3.45 2011 3.87 2012 3.45 2013 3.74 2014 4.38 2015 3.61 2016 4.31 2017 4.52 2018 4.74 2019 2.53 2020 2.23 2021 1.97