| Year | Value | | 2022 | 56.899079528885 | | 2021 | 56.4765116198 | | 2020 | 56.061754135014 | | 2019 | 55.627910531962 | | 2018 | 55.185236728143 | | 2017 | 54.73679896406 | | 2016 | 54.284287052529 | | 2015 | 53.825807191935 | | 2014 | 53.363490008655 | | 2013 | 52.908092990013 | | 2012 | 52.460841522624 | | 2011 | 52.021724727984 | | 2010 | 51.576293748566 | | 2009 | 51.087008609311 | | 2008 | 50.588399298439 | | 2007 | 50.081894386127 | | 2006 | 49.588314835903 | | 2005 | 49.088085518151 | | 2004 | 48.582934370787 | | 2003 | 48.08397565173 | | 2002 | 47.592622706251 | | 2001 | 47.103045123479 | | 2000 | 46.657857715198 | | 1999 | 46.277469659645 | | 1998 | 45.906120680305 | | 1997 | 45.53720498343 | | 1996 | 45.174620440505 | | 1995 | 44.817222756561 | | 1994 | 44.456850676825 | | 1993 | 44.095278320345 | | 1992 | 43.736686631251 | | 1991 | 43.372027776532 | | 1990 | 43.003909378413 | | 1989 | 42.644458826646 | | 1988 | 42.287792461893 | | 1987 | 41.920864730951 | | 1986 | 41.553932665034 | | 1985 | 41.189828710271 | | 1984 | 40.831842600715 | | 1983 | 40.476478023838 | | 1982 | 40.133642886225 | | 1981 | 39.755159458784 | | 1980 | 39.330137705147 | | 1979 | 38.915541177453 | | 1978 | 38.511833048601 | | 1977 | 38.176180003362 | | 1976 | 37.909994311796 | | 1975 | 37.649413316448 | | 1974 | 37.417813783422 | | 1973 | 37.153428401696 | | 1972 | 36.920174279684 | | 1971 | 36.707128947 | | 1970 | 36.505784106734 | | 1969 | 36.315829097833 | | 1968 | 36.119098116022 | | 1967 | 35.911333307247 | | 1966 | 35.698589604354 | | 1965 | 35.499521303861 | | 1964 | 35.282118255748 | | 1963 | 34.897986858294 | | 1962 | 34.52111956176 | | 1961 | 34.089565307991 | | 1960 | 33.602516003073 |
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