| Year | Value | | 2022 | 7.1722247601644 | | 2021 | 2.4983333333334 | | 2020 | 0.56813717711819 | | 2019 | 1.6107678729038 | | 2018 | 1.8129515654268 | | 2017 | 1.5855880170034 | | 2016 | 0.49174700844517 | | 2015 | 0.30936454849498 | | 2014 | 1.0251480303939 | | 2013 | 1.4782861568881 | | 2012 | 2.5853243284677 | | 2011 | 3.3355350880498 | | 2010 | 2.0200127009771 | | 2009 | 1.5618131744906 | | 2008 | 4.5521601685985 | | 2007 | 2.7717605872154 | | 2006 | 2.4959585126975 | | 2005 | 2.5601613233023 | | 2004 | 2.1420896464024 | | 2003 | 2.0527518015863 | | 2002 | 2.0575885809593 | | 2001 | 2.602128552459 | | 2000 | 2.6347446202118 | | 1999 | 1.943859844289 | | 1998 | 1.9550855771938 | | 1997 | 2.3376899373074 | | 1996 | 2.8517823639775 | | 1995 | 3.361391073209 | | 1994 | 2.7472905157407 | | 1993 | 4.0938362262872 | | 1992 | 4.0208478003856 | | 1991 | 5.0352743884811 | | 1990 | 5.4009577660463 | | 1989 | 5.0767934277426 | | 1988 | 4.4024118278676 | | 1987 | 3.6645632175169 | | 1986 | 2.9335792044233 | | 1985 | 4.6418805428719 | | 1984 | 5.9919511104844 | | 1983 | 6.9082288115884 | | 1982 | 8.8857130847146 | | 1981 | 11.427176323055 | | 1980 | 13.533381276113 |
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