| Year | Value | | 2022 | 0.88462434486087 | | 2021 | 0.90298888332359 | | 2020 | 0.96752416855618 | | 2019 | 1.0151345804293 | | 2018 | 1.0998600517024 | | 2017 | 1.1679505498019 | | 2016 | 1.1216080698576 | | 2015 | 1.1090565508692 | | 2014 | 1.1300137923582 | | 2013 | 1.1316897398536 | | 2012 | 1.1952449891029 | | 2011 | 1.203180620745 | | 2010 | 1.075189988456 | | 2009 | 1.0335636573502 | | 2008 | 1.1039755732697 | | 2007 | 1.1655972788639 | | 2006 | 1.221540411801 | | 2005 | 1.2750706232996 | | 2004 | 1.3435990065435 | | 2003 | 1.438786201094 | | 2002 | 1.5488140061677 | | 2001 | 1.6678432376059 | | 2000 | 1.8998718775249 | | 1999 | 2.1157377844919 | | 1998 | 2.1955988835016 | | 1997 | 2.2655522854659 | | 1996 | 2.3127237399279 | | 1995 | 2.39287120316 | | 1994 | 2.497218260716 | | 1993 | 2.5339473059185 | | 1992 | 2.4451705041192 | | 1991 | 2.2130774464263 | | 1990 | 1.7747482959399 | | 1989 | 1.3823997211526 | | 1988 | 1.2864323195625 | | 1987 | 1.2834434726453 | | 1986 | 1.2854177236733 | | 1985 | 1.3033484416975 | | 1984 | 1.3510718027405 | | 1983 | 1.4155327717723 | | 1982 | 1.4461177418287 | | 1981 | 1.3774581199179 | | 1980 | 1.0262609695961 | | 1979 | 0.73839997946399 | | 1978 | 0.73936775956105 | | 1977 | 0.77027784958999 | | 1976 | 0.86361124915886 | | 1975 | 0.88870113674922 | | 1974 | 0.82913170353624 | | 1973 | 0.79630090794537 | | 1972 | 1.1224481456374 | | 1971 | 2.1499983584958 | | 1970 | 3.0890459716259 | | 1969 | 3.3277272441701 | | 1968 | 3.3056121095457 | | 1967 | 3.2797751810975 | | 1966 | 3.2565720986796 | | 1965 | 3.244283715171 | | 1964 | 3.2455081665442 | | 1963 | 3.2559094331718 | | 1962 | 3.0698856960791 | | 1961 | 2.3263270692671 |
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