| Year | Value | | 2021 | 61.295108898696 | | 2020 | 61.676289018897 | | 2019 | 62.165886826599 | | 2018 | 61.864615206084 | | 2017 | 61.522082700142 | | 2016 | 61.192737005951 | | 2015 | 60.783603430493 | | 2014 | 60.472439976628 | | 2013 | 60.146122610746 | | 2012 | 59.934975811814 | | 2011 | 59.72027439198 | | 2010 | 59.230278542064 | | 2009 | 58.795389570304 | | 2008 | 58.196968985912 | | 2007 | 58.01148714294 | | 2006 | 57.724443087157 | | 2005 | 57.141507955308 | | 2004 | 56.790833675814 | | 2003 | 56.471563348936 | | 2002 | 56.07574144411 | | 2001 | 55.714176664225 | | 2000 | 55.340921460477 | | 1999 | 54.797539617106 | | 1998 | 53.805155862392 | | 1997 | 53.62652739306 | | 1996 | 53.282819645537 | | 1995 | 53.119353813355 | | 1994 | 52.964087255332 | | 1993 | 52.558317644056 | | 1992 | 52.273501390135 | | 1991 | 51.969525746244 | | 1990 | 52.163292258495 | | 1989 | 51.952603834111 | | 1988 | 51.2528670328 | | 1987 | 51.320721284259 | | 1986 | 51.015850132911 | | 1985 | 50.572778208701 | | 1984 | 50.294070519261 | | 1983 | 50.265519877557 | | 1982 | 50.455359255585 | | 1981 | 50.296917299638 | | 1980 | 49.954395256796 | | 1979 | 49.433325233015 | | 1978 | 49.060205184588 | | 1977 | 48.795185029071 | | 1976 | 48.330519656606 | | 1975 | 47.787104667364 | | 1974 | 47.544218271805 | | 1973 | 47.403820423402 | | 1972 | 46.880148827878 | | 1971 | 42.193600777028 | | 1970 | 45.525152081053 | | 1969 | 45.916499547026 | | 1968 | 45.575346104007 | | 1967 | 45.061358732234 | | 1966 | 44.748557894018 | | 1965 | 44.249861209867 | | 1964 | 44.064820724033 | | 1963 | 43.442553852472 | | 1962 | 43.157717786406 | | 1961 | 42.493837435384 | | 1960 | 41.992260159444 |
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