| Year | Value | | 2021 | 75.369193100344 | | 2020 | 75.203399321453 | | 2019 | 75.037605542563 | | 2018 | 74.872909735718 | | 2017 | 74.704920012736 | | 2016 | 74.542420149983 | | 2015 | 74.373332454956 | | 2014 | 74.215224480385 | | 2013 | 74.049430701494 | | 2012 | 73.885832866695 | | 2011 | 73.721137059851 | | 2010 | 73.557539225051 | | 2009 | 73.391745446161 | | 2008 | 73.230343555453 | | 2007 | 73.065647748608 | | 2006 | 72.902049913809 | | 2005 | 72.747235855375 | | 2004 | 72.579246132393 | | 2003 | 72.418942213731 | | 2002 | 72.255344378932 | | 2001 | 72.100530320498 | | 2000 | 71.925952765243 | | 1999 | 71.763452902489 | | 1998 | 71.59985506769 | | 1997 | 70.709399738683 | | 1996 | 70.533724211382 | | 1995 | 70.356950712035 | | 1994 | 67.984233121425 | | 1993 | 66.929081985573 | | 1992 | 66.5327140771 | | 1991 | 65.257968532121 | | 1990 | 64.466330687221 | | 1989 | 63.793273823248 | | 1988 | 63.642851652997 | | 1987 | 63.433138992281 | | 1986 | 63.342007312494 | | 1985 | 63.113629127002 | | 1984 | 62.774355764902 | | 1983 | 62.437278346893 | | 1982 | 62.318697365965 | | 1981 | 62.199018412991 | | 1980 | 62.080437432063 | | 1979 | 61.850961274526 | | 1978 | 61.512785884471 | | 1977 | 61.394204903543 | | 1976 | 61.525961549019 | | 1975 | 61.364559658311 | | 1974 | 61.203157767603 | | 1973 | 61.04065790485 | | 1972 | 60.879256014142 | | 1971 | 60.717854123434 | | 1970 | 60.555354260681 | | 1969 | 60.339053767691 | | 1968 | 60.06785467242 | | 1967 | 59.905354809666 | | 1966 | 60.183141737211 | | 1965 | 60.130439079021 | | 1964 | 59.969037188313 | | 1963 | 59.807635297605 | | 1962 | 59.645135434852 | | 1961 | 59.483733544144 |
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