| Year | Value | | 2022 | 1.5953807433314 | | 2021 | 1.6130738643313 | | 2020 | 1.7566994709884 | | 2019 | 1.682911011513 | | 2018 | 1.6735782094454 | | 2017 | 1.7112426438885 | | 2016 | 1.7688865902507 | | 2015 | 1.7767710689681 | | 2014 | 1.7384092879439 | | 2013 | 1.7143409229625 | | 2012 | 1.7009426716012 | | 2011 | 1.659082515957 | | 2010 | 1.7335198621283 | | 2009 | 1.8935237960352 | | 2008 | 1.716042545805 | | 2007 | 1.7501645854519 | | 2006 | 1.8695916362794 | | 2005 | 1.8718580229483 | | 2004 | 1.938508232798 | | 2003 | 1.9962889356584 | | 2002 | 2.0593646529375 | | 2001 | 1.983086243658 | | 2000 | 1.8357596845419 | | 1999 | 1.8714659141258 | | 1998 | 1.6550806909055 | | 1997 | 1.6326506728454 | | 1996 | 1.6527266700096 | | 1995 | 1.6862338869154 | | 1994 | 1.6934795987048 | | 1993 | 1.9280668740406 | | 1992 | 2.4495420675344 | | 1991 | 2.3112434115531 | | 1990 | 2.4540161155274 | | 1989 | 2.4471013153258 |
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