| Year | Value | | 2024 | 1.9225523127637 | | 2023 | 1.7199188018747 | | 2022 | 1.6587984353461 | | 2021 | 1.8588832109146 | | 2020 | 2.1955521869102 | | 2019 | 2.6898589794363 | | 2018 | 2.5220902241486 | | 2017 | 2.0500659921933 | | 2016 | 2.050324378655 | | 2015 | 1.8128485572373 | | 2014 | 1.871966394439 | | 2013 | 1.9239596649605 | | 2012 | 2.0094481178694 | | 2011 | 2.0275060358965 | | 2010 | 2.2717151509338 | | 2009 | 2.471551275274 | | 2008 | 2.1817869950417 | | 2007 | 2.1998066044665 | | 2006 | 2.3401613381772 | | 2005 | 2.38609105307 | | 2004 | 2.6710002937277 | | 2003 | 3.2670311950015 | | 2002 | 3.7670915104156 | | 2001 | 3.5766797079423 | | 2000 | 3.6434293404675 | | 1999 | 3.8814129638098 | | 1998 | 3.1822080014233 | | 1997 | 4.1036722305683 | | 1996 | 4.1396969426189 | | 1995 | 3.901649734749 | | 1994 | 4.051359336992 | | 1993 | 3.9214172544983 | | 1992 | 3.8705665002104 | | 1991 | 3.7543642480797 | | 1990 | 3.5277056937872 | | 1989 | 3.1487265209167 | | 1988 | 2.932208636434 | | 1987 | 3.3285852504838 | | 1986 | 3.6379924825209 | | 1985 | 3.5310431587826 | | 1984 | 3.5970938149502 | | 1983 | 3.9376052054601 | | 1982 | 4.2981513121269 | | 1981 | 3.8245318699791 | | 1980 | 3.9003132966797 | | 1979 | 3.3572585580073 | | 1978 | 4.1873064036918 | | 1977 | 4.7136230237622 | | 1976 | 4.9430272108843 |
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