| Year | Value | | 2022 | 1.3207851744045 | | 2021 | 1.4583380806692 | | 2020 | 1.4082889871097 | | 2019 | 1.364983236218 | | 2018 | 1.4731803877656 | | 2017 | 1.5632876903471 | | 2016 | 1.4959940602137 | | 2015 | 1.5129258383029 | | 2014 | 1.5156182958474 | | 2013 | 1.5375486581941 | | 2012 | 1.5790413844891 | | 2011 | 1.5613881695106 | | 2010 | 1.9612551606509 | | 2009 | 2.1417717640998 | | 2008 | 2.0307352958606 | | 2007 | 2.0887605503202 | | 2006 | 2.0753551559057 | | 2005 | 2.2624047145916 | | 2004 | 2.5302044928523 | | 2003 | 2.57470164782 | | 2002 | 2.7149205071419 | | 2001 | 2.737540750499 | | 2000 | 2.8016923195226 | | 1999 | 3.0356455769787 | | 1998 | 2.3549176985297 | | 1997 | 2.2247668381867 | | 1996 | 2.3326752128247 | | 1995 | 2.6819724308426 | | 1994 | 3.3370577628055 | | 1993 | 3.3980682015318 | | 1992 | 3.502455695642 | | 1991 | 3.69206415923 | | 1990 | 3.4193952011374 | | 1989 | 3.2882401311585 | | 1988 | 3.2388811439205 | | 1987 | 3.8088444456544 | | 1986 | 4.1058717482534 | | 1985 | 3.9208414325088 | | 1984 | 4.0367149024838 | | 1983 | 3.8609926829385 | | 1982 | 3.6197219874247 | | 1981 | 3.4916952399952 | | 1980 | 3.8728468747874 | | 1979 | 4.0886992019571 | | 1978 | 4.2508537003987 | | 1977 | 4.4088521538825 | | 1976 | 4.4004805531527 | | 1975 | 4.4558755406939 | | 1974 | 3.3641552396984 | | 1973 | 3.5605122325636 | | 1972 | 4.4597222889849 | | 1971 | 4.0187631886216 | | 1970 | 4.1530337536011 |
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