| Year | Value | | 2021 | 5.1117179407848 | | 2020 | 5.1117179407848 | | 2019 | 5.1117179407848 | | 2018 | 5.1117179407848 | | 2017 | 5.1117179407848 | | 2016 | 4.9771990476062 | | 2015 | 4.9771990476062 | | 2014 | 4.9771990476062 | | 2013 | 4.9771990476062 | | 2012 | 5.1117179407848 | | 2011 | 4.8426801544277 | | 2010 | 4.5736423680706 | | 2009 | 4.7754207078384 | | 2008 | 4.1055166198092 | | 2007 | 3.9669621598353 | | 2006 | 4.0530542514696 | | 2005 | 3.668330216979 | | 2004 | 3.84993072277 | | 2003 | 3.8660729899514 | | 2002 | 3.4732778218701 | | 2001 | 3.6616042723201 | | 2000 | 3.8257173219979 | | 1999 | 3.8257173219979 | | 1998 | 3.8257173219979 | | 1997 | 3.8257173219979 | | 1996 | 3.8257173219979 | | 1995 | 3.8257173219979 | | 1994 | 3.8337884555886 | | 1993 | 3.7396252303636 | | 1992 | 3.7382800414318 | | 1991 | 3.705995507069 | | 1990 | 3.8889412017918 | | 1989 | 3.8889412017918 | | 1988 | 3.7382800414318 | | 1987 | 3.6629494612518 | | 1986 | 3.5876188810719 | | 1985 | 3.5136334898237 | | 1984 | 3.4383029096437 | | 1983 | 3.3629723294637 | | 1982 | 3.2876417492837 | | 1981 | 3.2123111691037 | | 1980 | 3.1369805889237 | | 1979 | 3.1020056766973 | | 1978 | 3.6616042723201 | | 1977 | 3.8754893124739 | | 1976 | 3.9050834689732 | | 1975 | 3.9346776254725 | | 1974 | 3.9548554594493 | | 1973 | 3.9171901693593 | | 1972 | 3.9037382800414 | | 1971 | 3.8902863907236 | | 1970 | 3.7167570185232 | | 1969 | 3.6777465395015 | | 1968 | 3.6387360604797 | | 1967 | 3.5943448257308 | | 1966 | 3.5755121806858 | | 1965 | 3.5028719783694 | | 1964 | 3.498836411574 | | 1963 | 3.4652066882794 | | 1962 | 3.4329221539165 | | 1961 | 3.4288865871212 |
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