| Year | Value | | 2022 | 1.1576408457647 | | 2021 | 1.3061276571085 | | 2020 | 1.4545186763788 | | 2019 | 1.3513850303183 | | 2018 | 1.3569299238885 | | 2017 | 1.3897647983067 | | 2016 | 1.4216601028475 | | 2015 | 1.4265803023078 | | 2014 | 1.4066360218728 | | 2013 | 1.4039567766839 | | 2012 | 1.3814113291659 | | 2011 | 1.4867041004229 | | 2010 | 1.4548083287581 | | 2009 | 1.7037553019755 | | 2008 | 1.5326886598223 | | 2007 | 1.3396974517047 | | 2006 | 1.1011616129091 | | 2005 | 1.0482294690948 | | 2004 | 1.0798069272825 | | 2003 | 1.2421279685537 | | 2002 | 1.3499492510544 | | 2001 | 1.4337874388706 | | 2000 | 1.4882309500746 | | 1999 | 1.6237976325211 | | 1998 | 1.8563682812446 | | 1997 | 2.1739225047072 | | 1996 | 2.1515250813553 | | 1995 | 2.2737823729037 | | 1994 | 2.5023833534472 | | 1993 | 2.524824498771 | | 1992 | 2.6574228781558 | | 1991 | 2.6450248140938 | | 1990 | 2.5942501889126 | | 1989 | 2.6846671226016 | | 1988 | 2.9335010898833 | | 1987 | 3.3613865575309 | | 1986 | 3.7953282159873 | | 1985 | 4.1891150023663 | | 1984 | 4.0644387543393 | | 1983 | 3.9533588349047 | | 1982 | 4.1203692151208 | | 1981 | 4.0631625186097 | | 1980 | 4.2444549436815 | | 1979 | 4.3809194057199 | | 1978 | 3.9237142330459 | | 1977 | 3.4817733501846 | | 1976 | 3.1314209858017 | | 1975 | 2.7952327574838 | | 1974 | 2.6554385587909 |
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