| Year | Value | | 2022 | 1.8147966516279 | | 2021 | 1.9074600234849 | | 2020 | 1.9369810234778 | | 2019 | 1.7867447443773 | | 2018 | 1.7605459168691 | | 2017 | 1.5681029390755 | | 2016 | 1.4045576122121 | | 2015 | 1.6476676274439 | | 2014 | 1.5426019597892 | | 2013 | 1.6070090895153 | | 2012 | 1.6547517020963 | | 2011 | 1.7378320909756 | | 2010 | 1.8529245505669 | | 2009 | 1.8168195077902 | | 2008 | 1.6297049444975 | | 2007 | 1.6845996583175 | | 2006 | 1.8999978625024 | | 2005 | 2.037469743237 | | 2004 | 1.9557691617927 | | 2003 | 1.9851631243572 | | 2002 | 2.1301607353618 | | 2001 | 3.1532221594789 | | 2000 | 2.8220901513395 | | 1999 | 2.7338509695516 | | 1998 | 4.6763179459164 | | 1997 | 5.573910769889 | | 1996 | 4.5247148288973 | | 1995 | 3.0410342149261 | | 1994 | 4.0239891959577 | | 1993 | 4.0749526049948 | | 1992 | 9.1292860441849 | | 1991 | 7.2647761224664 | | 1990 | 7.3740356129737 | | 1989 | 5.3693550975342 | | 1988 | 5.7002560291446 | | 1987 | 5.3914776975487 | | 1986 | 1.5771578985852 | | 1985 | 1.2702916956171 |
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