Year % 1992 5.1 1993 4.6 1996 4 2002 4 2004 3.6 2005 3.8 2006 3.7 2007 3.9 2008 3.9 2009 3.8 2010 3.7 2011 3.7 2012 3.9 2013 3.8 2014 3.9 2015 3.9 2016 4 2017 4.2 2018 4.2 2019 4.2 2020 4 2021 3.9