| Year | Value | | 2022 | 1.9222756165965 | | 2021 | 1.8803436990579 | | 2020 | 1.9097931149719 | | 2019 | 1.7575221345214 | | 2018 | 1.6285184501573 | | 2017 | 1.5358659619577 | | 2016 | 1.4854402538529 | | 2015 | 1.5338083021728 | | 2014 | 1.4225445649322 | | 2013 | 1.3777545498526 | | 2012 | 1.3905229026837 | | 2011 | 1.4023749847028 | | 2010 | 1.4718421096999 | | 2009 | 1.5210463366276 | | 2008 | 1.5294015520576 | | 2007 | 1.6513707483322 | | 2006 | 1.693995507116 | | 2005 | 1.7733338547799 | | 2004 | 1.7519888728099 | | 2003 | 1.8592475054124 | | 2002 | 1.8936322610412 | | 2001 | 1.8914368528156 | | 2000 | 1.8601859045597 | | 1999 | 1.9534566881932 | | 1998 | 2.1161594335419 | | 1997 | 2.2495060560166 | | 1996 | 2.2421843687077 | | 1995 | 2.3644515041688 | | 1994 | 2.2801298410483 | | 1993 | 2.3505053290596 | | 1992 | 2.5653421969183 | | 1991 | 2.740756475848 | | 1990 | 3.4069729280745 | | 1989 | 4.6582981301306 |
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