| Year | Value | | 2024 | 0.781 | | 2023 | 0.733 | | 2022 | 0.94 | | 2021 | 1.215 | | 2020 | 1.099 | | 2019 | 0.716 | | 2018 | 0.765 | | 2017 | 0.83 | | 2016 | 0.688 | | 2015 | 0.597 | | 2014 | 0.576 | | 2013 | 0.249 | | 2012 | 0.58 | | 2011 | 0.66 | | 2010 | 0.622 | | 2009 | 1.49 | | 2008 | 1.18 | | 2007 | 1.18 | | 2006 | 1.22 | | 2005 | 1.35 | | 2004 | 1.51 | | 2003 | 1.54 | | 2001 | 2.6 | | 2000 | 2.389 | | 1999 | 2.968 | | 1998 | 3.404 | | 1997 | 0.873 | | 1996 | 1.071 | | 1995 | 1.1 | | 1994 | 1.347 | | 1993 | 1.49 | | 1992 | 1.35 | | 1991 | 2.63 | | 1990 | 2.21 | | 1989 | 1.39 | | 1988 | 3.04 | | 1987 | 5.77 | | 1986 | 3.5 | | 1985 | 4.93 | | 1984 | 2.9 | | 1983 | 2.9 | | 1982 | 2.66 | | 1981 | 1.26 | | 1980 | 0.93 | | 1979 | 0.92 | | 1978 | 0.75 | | 1977 | 0.9 | | 1976 | 0.6 | | 1975 | 0.45 |
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