| Year | Value | | 2022 | 3.5409256822144 | | 2021 | 3.5050358243644 | | 2020 | 3.0669862508844 | | 2019 | 2.7136236599052 | | 2018 | 3.0545153835992 | | 2017 | 3.9349472922118 | | 2016 | 4.3963458782793 | | 2015 | 4.2737448873365 | | 2014 | 4.1850650433225 | | 2013 | 4.6234689301284 | | 2012 | 4.8798135551174 | | 2011 | 4.7819288006268 | | 2010 | 4.6541617352099 | | 2009 | 4.3750527052031 | | 2008 | 5.4449525528258 | | 2007 | 5.7590717900346 | | 2006 | 5.9771245849219 | | 2005 | 6.5811652620007 | | 2004 | 6.0821388120885 | | 2003 | 6.6672673624974 | | 2002 | 8.2949161079441 | | 2001 | 10.534568781183 | | 2000 | 9.4267765145751 | | 1999 | 9.5287210280321 | | 1998 | 15.955695863482 | | 1997 | 12.220800451728 | | 1996 | 9.678382318418 | | 1995 | 10.60868616027 | | 1994 | 26.352037210737 | | 1993 | 25.894576910824 | | 1992 | 20.471418696011 | | 1991 | 20.250415714383 | | 1990 | 23.724359442295 |
|