| Year | Value | | 2021 | 65.6127558191 | | 2020 | 65.923252255997 | | 2019 | 66.341822949901 | | 2018 | 65.982366643392 | | 2017 | 65.659891422448 | | 2016 | 65.239643080367 | | 2015 | 64.83065759511 | | 2014 | 64.485078533557 | | 2013 | 64.210613992517 | | 2012 | 63.728575970279 | | 2011 | 63.295256598064 | | 2010 | 62.671400756286 | | 2009 | 62.21787554574 | | 2008 | 61.460020976936 | | 2007 | 61.281630735208 | | 2006 | 60.860175355535 | | 2005 | 60.164535490525 | | 2004 | 59.666407433653 | | 2003 | 59.34737251986 | | 2002 | 58.851074119496 | | 2001 | 58.393508566714 | | 2000 | 58.003131683582 | | 1999 | 57.683082268993 | | 1998 | 56.808996138527 | | 1997 | 56.488092374758 | | 1996 | 55.943018747309 | | 1995 | 55.826426562706 | | 1994 | 55.5827439258 | | 1993 | 55.318620933337 | | 1992 | 55.108306110783 | | 1991 | 54.765171164222 | | 1990 | 55.05599344684 | | 1989 | 54.795979825181 | | 1988 | 54.253707589125 | | 1987 | 54.248069475017 | | 1986 | 53.823153195086 | | 1985 | 53.432402234793 | | 1984 | 53.24423476236 | | 1983 | 52.976090051679 | | 1982 | 53.19510781238 | | 1981 | 52.889477555223 | | 1980 | 52.467396730033 | | 1979 | 51.997720833068 | | 1978 | 51.5117186797 | | 1977 | 51.003285044948 | | 1976 | 50.304686004902 | | 1975 | 49.720400718812 | | 1974 | 49.583281888457 | | 1973 | 49.513313012201 | | 1972 | 48.986210626557 | | 1971 | 46.484979925245 | | 1970 | 47.436995929733 | | 1969 | 47.97721403781 | | 1968 | 47.616700051675 | | 1967 | 47.100227477739 | | 1966 | 46.538308471724 | | 1965 | 46.068724197131 | | 1964 | 45.87540131466 | | 1963 | 45.176699543952 | | 1962 | 44.817472616832 | | 1961 | 44.334243460398 | | 1960 | 43.807117026663 |
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