| Year | Value | | 2022 | 1.5291192295428 | | 2021 | 1.5984700138319 | | 2020 | 1.5158211407513 | | 2019 | 1.4627271241997 | | 2018 | 1.4858082268632 | | 2017 | 1.5133624348431 | | 2016 | 1.542920080054 | | 2015 | 1.755472385901 | | 2014 | 1.9839679711552 | | 2013 | 2.07720395196 | | 2012 | 2.1950076430375 | | 2011 | 2.224976884518 | | 2010 | 2.1306026960996 | | 2009 | 2.1307672817853 | | 2008 | 2.2997098695071 | | 2007 | 2.4627770211528 | | 2006 | 2.5716877021051 | | 2005 | 2.435663207176 | | 2004 | 2.0578391686051 | | 2003 | 1.8604731884622 | | 2002 | 1.8460116809922 | | 2001 | 1.653116831891 | | 2000 | 1.3422481859481 | | 1999 | 1.3054333387351 | | 1998 | 1.4208333209734 | | 1997 | 1.4417935069524 | | 1996 | 1.4593456788856 | | 1995 | 1.4893830847604 | | 1994 | 1.489891467229 | | 1993 | 1.453457251214 | | 1992 | 1.4200038136686 | | 1991 | 1.9009418340036 | | 1990 | 2.4531203600002 | | 1989 | 2.3311652761022 | | 1988 | 2.0872482205266 | | 1987 | 1.927575280089 | | 1986 | 1.7642657067028 | | 1985 | 1.5864599859782 | | 1984 | 1.3437150411112 | | 1983 | 1.1081505464852 | | 1982 | 0.8988362841278 | | 1981 | 1.0880698050395 | | 1980 | 1.2022642157474 | | 1979 | 1.0898366492985 | | 1978 | 1.3413418170991 | | 1977 | 1.5717703664739 | | 1976 | 1.5745388837041 | | 1975 | 1.3165202313421 | | 1974 | 1.4013518316556 | | 1973 | 1.7307126273224 | | 1972 | 1.7682871573721 | | 1971 | 1.7768322526262 | | 1970 | 1.7808591286664 | | 1969 | 1.7783544060961 | | 1968 | 1.7690425609817 | | 1967 | 1.7431555641871 | | 1966 | 1.7037085874828 | | 1965 | 1.6572785983874 | | 1964 | 1.6196215094173 | | 1963 | 1.5995152398624 | | 1962 | 1.5698045275369 | | 1961 | 1.5297284964077 |
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