Year % 1997 8 1998 6.8 1999 8 2000 12.38 2001 13.95 2002 13.77 2003 12.05 2004 11.76 2005 15.04 2006 16.29 2007 17.74 2008 22.12 2009 26.06 2010 24.96 2011 23.97 2012 23.31 2013 24.61 2015 29.06 2016 30.74 2017 31.39 2018 29.99 2019 31 2020 30.67 2021 31.41