Year | Value | 2022 | 19.238003689219 | 2021 | 15.594465710609 | 2020 | 21.075519516848 | 2019 | 17.590638787666 | 2018 | 19.997883431346 | 2017 | 15.859632438143 | 2016 | 18.635197269284 | 2015 | 21.10305219429 | 2014 | 18.232905214333 | 2013 | 15.127461177222 | 2012 | 5.2675191854576 | 2011 | 3.8817620783489 | 2010 | 4.8708608291523 | 2009 | 11.036203355483 | 2008 | 4.3409738696277 | 2007 | 6.7437820573154 | 2006 | 17.411536288962 | 2005 | 19.207310517403 | 2004 | 22.871691477471 | 2003 | 21.156288220358 | 2002 | 18.754322731366 | 2001 | 21.092722099935 | 2000 | 15.265862335031 | 1999 | 9.3631922710619 | 1998 | 18.031633175301 | 1997 | 10.410867657687 | 1996 | 18.095309859155 | 1995 | 17.625605325284 | 1994 | 19.077268472622 | 1993 | 12.836353012577 | 1992 | 6.9325444409758 | 1991 | 11.86260172381 | 1990 | 10.533404206913 | 1989 | 11.40509866541 | 1988 | 9.9640980369027 | 1987 | 7.5708579088472 | 1986 | 6.9286196721504 | 1985 | 8.0342062918309 | 1984 | 6.7457009694671 | 1983 | 4.2568643432335 | 1982 | 5.5549155012666 | 1981 | 5.7033569245174 | 1980 | 6.3240548865864 | 1979 | 8.2553792011913 | 1978 | 5.4083981276263 | 1977 | 11.482818469411 | 1976 | 8.7681168274451 | 1975 | 14.436898162386 |
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