| Year | Value | | 2021 | 58.263177180715 | | 2020 | 58.901632041724 | | 2019 | 59.363448490691 | | 2018 | 59.010095442338 | | 2017 | 58.656774868182 | | 2016 | 58.261180907267 | | 2015 | 57.765294689696 | | 2014 | 57.366366085812 | | 2013 | 56.94089722729 | | 2012 | 56.493264963641 | | 2011 | 55.966366170324 | | 2010 | 55.324748199792 | | 2009 | 54.727772443271 | | 2008 | 54.041573261277 | | 2007 | 53.461379636903 | | 2006 | 52.867434225818 | | 2005 | 52.113782203557 | | 2004 | 51.508948712043 | | 2003 | 51.011464827588 | | 2002 | 50.487215371333 | | 2001 | 50.121450287015 | | 2000 | 49.764445145598 | | 1999 | 48.868725599202 | | 1998 | 48.091032148925 | | 1997 | 48.418782556869 | | 1996 | 48.204851218829 | | 1995 | 48.250850636021 | | 1994 | 48.169360210346 | | 1993 | 47.69824852195 | | 1992 | 47.497850718473 | | 1991 | 47.744625671799 | | 1990 | 47.795778681831 | | 1989 | 47.928369906871 | | 1988 | 46.996040514445 | | 1987 | 47.333895758794 | | 1986 | 47.121612080795 | | 1985 | 46.751218414116 | | 1984 | 46.520368301597 | | 1983 | 46.586212529624 | | 1982 | 47.430981693103 | | 1981 | 47.220176336217 | | 1980 | 46.88067389891 | | 1979 | 46.51209710182 | | 1978 | 46.024703404197 | | 1977 | 45.80733813019 | | 1976 | 45.405262947701 | | 1975 | 44.817958491904 | | 1974 | 44.432481129887 | | 1973 | 44.211278705831 | | 1972 | 43.417323191668 | | 1971 | 43.296874985588 | | 1970 | 42.804827774354 | | 1969 | 42.248357847764 | | 1968 | 42.010892654184 | | 1967 | 41.563347308286 | | 1966 | 41.470090133684 | | 1965 | 41.471011409073 | | 1964 | 41.338801166199 | | 1963 | 40.921327142313 | | 1962 | 40.756156123974 | | 1961 | 40.193582924116 | | 1960 | 39.936486093579 |
|