| Year | Value | | 2021 | 0.36556091559914 | | 2020 | 0.45453618687092 | | 2019 | 0.37863816830353 | | 2018 | 0.37477663312666 | | 2017 | 0.42377629363822 | | 2016 | 0.46032912801972 | | 2015 | 0.44372964310715 | | 2014 | 0.40257431413765 | | 2013 | 0.37288280327133 | | 2012 | 0.30163541783616 | | 2011 | 0.30987225358116 | | 2010 | 0.34430349226214 | | 2009 | 0.33618722456831 | | 2008 | 0.29848081096673 | | 2007 | 0.30479432418649 | | 2006 | 0.27890280541574 | | 2005 | 0.2872670393918 | | 2004 | 0.32223657569386 | | 2003 | 0.37129950064977 | | 2002 | 0.37863704799761 | | 2001 | 0.43215021080498 | | 2000 | 0.4829633678248 | | 1999 | 0.76634838575256 | | 1998 | 0.92867929536593 | | 1997 | 0.89992958986094 | | 1996 | 0.95304113604405 | | 1995 | 1.2267059019989 | | 1994 | 0.98725690208421 | | 1993 | 1.0018040365317 | | 1992 | 0.98275872294745 | | 1991 | 0.96849885610371 | | 1990 | 0.88385893310966 | | 1989 | 0.76768289321352 | | 1988 | 0.90332578862584 | | 1987 | 0.97660807018246 | | 1986 | 0.8498051551716 | | 1985 | 0.69100788733175 | | 1984 | 0.70179392046872 | | 1983 | 0.76700172054695 | | 1982 | 0.8080354089519 | | 1981 | 0.90380621392864 | | 1980 | 0.87199119251364 | | 1979 | 0.97598475859418 | | 1978 | 1.138776660716 | | 1977 | 1.4674837572503 | | 1976 | 1.5274225632282 | | 1975 | 1.8953558073816 | | 1974 | 2.1058789119626 | | 1973 | 2.2245368648166 | | 1972 | 2.0953977445901 |
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