| Year | Value | | 2021 | 4.7796803652968 | | 2020 | 4.8333073889581 | | 2019 | 4.8869344126193 | | 2018 | 4.9405614362806 | | 2017 | 4.9941884599419 | | 2016 | 5.0179535076795 | | 2015 | 5.1014425072644 | | 2014 | 5.14324667912 | | 2013 | 5.1850508509755 | | 2012 | 5.2268550228311 | | 2011 | 5.2686591946866 | | 2010 | 5.3104633665421 | | 2009 | 5.3646261415525 | | 2008 | 5.4187889165629 | | 2007 | 5.4729516915733 | | 2006 | 5.5271144665836 | | 2005 | 5.581277241594 | | 2004 | 5.6354400166044 | | 2003 | 5.6896027916148 | | 2002 | 5.7437655666252 | | 2001 | 5.7979283416355 | | 2000 | 5.8520911166459 | | 1999 | 5.9137777604815 | | 1998 | 5.9754644043171 | | 1997 | 6.0371510481528 | | 1996 | 6.0988376919884 | | 1995 | 6.160524335824 | | 1994 | 6.2222109796596 | | 1993 | 6.2838976234952 | | 1992 | 6.3455842673308 | | 1991 | 6.4072709111665 | | 1990 | 6.4689575550021 |
|