| Year | Value | | 2021 | 64.747785142693 | | 2020 | 65.105904830407 | | 2019 | 65.64179339729 | | 2018 | 65.277193059858 | | 2017 | 64.872728648715 | | 2016 | 64.471642932639 | | 2015 | 63.957889205789 | | 2014 | 63.577512752047 | | 2013 | 63.194095758724 | | 2012 | 62.848514616804 | | 2011 | 62.47195235985 | | 2010 | 61.82728354619 | | 2009 | 61.327357448225 | | 2008 | 60.475320378923 | | 2007 | 60.345755835722 | | 2006 | 59.940844810419 | | 2005 | 59.385105371071 | | 2004 | 58.77087881921 | | 2003 | 58.450820057071 | | 2002 | 57.947181602394 | | 2001 | 57.51218718264 | | 2000 | 57.06333768301 | | 1999 | 56.606406481422 | | 1998 | 55.410054532511 | | 1997 | 55.176868655333 | | 1996 | 54.540272643931 | | 1995 | 54.408090046001 | | 1994 | 53.99568703624 | | 1993 | 53.410057244377 | | 1992 | 52.945070525766 | | 1991 | 52.37152992807 | | 1990 | 52.650549140271 | | 1989 | 52.347493641803 | | 1988 | 51.463713313007 | | 1987 | 51.584941334852 | | 1986 | 51.019108099708 | | 1985 | 50.393377226513 | | 1984 | 50.043133861048 | | 1983 | 49.93978617227 | | 1982 | 50.411612845019 | | 1981 | 50.197083494238 | | 1980 | 49.905340338432 | | 1979 | 49.409353536915 | | 1978 | 48.948019793472 | | 1977 | 48.580066241163 | | 1976 | 47.913226735067 | | 1975 | 47.305138691752 | | 1974 | 47.2611641325 | | 1973 | 47.254480959814 | | 1972 | 46.69392040985 | | 1971 | 42.290826064038 | | 1970 | 45.048774352959 | | 1969 | 46.137928089585 | | 1968 | 45.881401293024 | | 1967 | 45.515423868818 | | 1966 | 44.940437767811 | | 1965 | 44.554538377151 | | 1964 | 44.532066365068 | | 1963 | 43.843503963049 | | 1962 | 43.688619024047 | | 1961 | 43.192342117782 | | 1960 | 42.720180046496 |
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