| Year | Value | | 2022 | 21.400669814969 | | 2021 | 21.508246801907 | | 2020 | 21.858321160062 | | 2019 | 21.319356379743 | | 2018 | 20.639792111348 | | 2017 | 19.73731832404 | | 2016 | 18.134421604671 | | 2015 | 18.826862585322 | | 2014 | 23.084178464892 | | 2013 | 21.221235047264 | | 2012 | 18.184333456884 | | 2011 | 18.305165181906 | | 2010 | 18.325282621786 | | 2009 | 14.727180637569 | | 2008 | 14.907833201995 | | 2007 | 17.001570756142 | | 2006 | 16.354418463496 | | 2005 | 16.868273787732 | | 2004 | 15.07115200973 | | 2003 | 15.259877038021 | | 2002 | 15.671969601307 | | 2001 | 14.370915571502 | | 2000 | 12.94999289965 | | 1999 | 10.513438696346 | | 1998 | 12.830285286494 | | 1997 | 14.923611444636 | | 1996 | 12.492171369217 | | 1995 | 13.382124400233 |
|