| Year | Value | | 2023 | 0.40638935111866 | | 2022 | 0.98458624446936 | | 2021 | 0.91044490256451 | | 2020 | 0.97038603135316 | | 2019 | 1.4296968810979 | | 2018 | 1.3536029864843 | | 2017 | 1.2967557122046 | | 2016 | 1.3454259350487 | | 2015 | 1.3341157703041 | | 2014 | 1.3490889002021 | | 2013 | 1.28441474668 | | 2012 | 1.2747180198131 | | 2011 | 1.4677741644914 | | 2010 | 1.5194309376329 | | 2009 | 1.3803027157145 | | 2008 | 1.2656033653568 | | 2007 | 0.16085626347595 | | 2006 | 1.0271551943198 | | 2005 | 1.0686418170443 | | 2004 | 1.1154825461705 | | 2003 | 1.1609441668303 | | 2002 | 1.2058715363738 | | 2001 | 1.2442785656482 | | 2000 | 1.2829764871256 | | 1999 | 1.3365190532942 | | 1998 | 1.3926055829745 | | 1997 | 1.4452212656733 | | 1996 | 1.5070440949697 | | 1995 | 1.6367135437877 | | 1994 | 1.7385011442805 | | 1993 | 1.7250708442112 | | 1992 | 1.7047907786747 | | 1991 | 1.7593985702591 | | 1990 | 1.8720845761971 | | 1989 | 1.9600825517456 | | 1988 | 1.9971119750501 | | 1987 | 2.0376986999168 | | 1986 | 2.1289208915688 | | 1985 | 2.2203841683057 | | 1984 | 2.2989014867145 | | 1983 | 2.3501547438948 | | 1982 | 2.1377808515577 | | 1981 | 1.989327458532 | | 1980 | 1.9982727930855 | | 1979 | 1.9627781989727 | | 1978 | 2.0181709885216 | | 1977 | 2.0628584323459 | | 1976 | 2.0418461032027 | | 1975 | 2.0745443694269 |
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