| Year | Value | | 2021 | 54.046402502607 | | 2020 | 54.055265901981 | | 2019 | 54.058394160584 | | 2018 | 54.070907194995 | | 2017 | 54.953597497393 | | 2016 | 54.958811261731 | | 2015 | 55.037539103232 | | 2014 | 55.042231491137 | | 2013 | 55.040145985402 | | 2012 | 55.220542231491 | | 2011 | 55.310218978102 | | 2010 | 55.327945776851 | | 2009 | 55.356100104275 | | 2008 | 55.929092805005 | | 2007 | 55.936392075078 | | 2006 | 55.949426485923 | | 2005 | 56.021897810219 | | 2004 | 56.152241918665 | | 2003 | 56.517205422315 | | 2002 | 56.183524504692 | | 2001 | 56.183524504692 | | 2000 | 55.860271115746 | | 1999 | 55.9228362878 | | 1998 | 55.735140771637 | | 1997 | 55.583941605839 | | 1996 | 55.479666319082 | | 1995 | 54.937434827946 | | 1994 | 53.852971845673 | | 1993 | 52.763295099062 | | 1992 | 52.59645464025 |
|