| Year | Value | | 2022 | 50.297580040644 | | 2021 | 50.310535618948 | | 2020 | 50.317487275415 | | 2019 | 50.330398746503 | | 2018 | 50.34953634846 | | 2017 | 50.371524753769 | | 2016 | 50.394344245279 | | 2015 | 50.416302180369 | | 2014 | 50.436776844466 | | 2013 | 50.454760178124 | | 2012 | 50.471451238372 | | 2011 | 50.487561814911 | | 2010 | 50.499475931956 | | 2009 | 50.505339555477 | | 2008 | 50.510887400772 | | 2007 | 50.513500144467 | | 2006 | 50.513451907691 | | 2005 | 50.514065728515 | | 2004 | 50.513523834692 | | 2003 | 50.514978100557 | | 2002 | 50.520276464404 | | 2001 | 50.527655616734 | | 2000 | 50.535057410356 | | 1999 | 50.544338787441 | | 1998 | 50.55350917285 | | 1997 | 50.561663682537 | | 1996 | 50.569124045539 | | 1995 | 50.574894210195 | | 1994 | 50.581368304512 | | 1993 | 50.585997613547 | | 1992 | 50.587653297524 | | 1991 | 50.587502120082 | | 1990 | 50.584574387931 | | 1989 | 50.577455897133 | | 1988 | 50.565710615365 | | 1987 | 50.550983588003 | | 1986 | 50.53310491511 | | 1985 | 50.511983435319 | | 1984 | 50.488754028462 | | 1983 | 50.462659242777 | | 1982 | 50.434164702729 | | 1981 | 50.404999030056 | | 1980 | 50.374409419926 | | 1979 | 50.343315631653 | | 1978 | 50.311547271397 | | 1977 | 50.279901954204 | | 1976 | 50.248537221209 | | 1975 | 50.216397592822 | | 1974 | 50.188303821709 | | 1973 | 50.164215542288 | | 1972 | 50.1412545136 | | 1971 | 50.123381780083 | | 1970 | 50.111200714605 | | 1969 | 50.105265413315 | | 1968 | 50.103447733987 | | 1967 | 50.103995661275 | | 1966 | 50.110483103959 | | 1965 | 50.120843536681 | | 1964 | 50.133320085636 | | 1963 | 50.146160674303 | | 1962 | 50.157335248704 | | 1961 | 50.168875077088 | | 1960 | 50.180947431406 |
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