| Year | Value | | 2022 | 4.995020750609 | | 2021 | 2.9658100834628 | | 2020 | 1.6122222040245 | | 2019 | 1.04883403679 | | 2018 | 2.7627507703294 | | 2017 | 2.0693292816443 | | 2016 | 2.3727160307583 | | 2015 | 1.8313523315637 | | 2014 | 2.6475532124619 | | 2013 | 3.2381083391407 | | 2012 | 4.6118443220664 | | 2011 | 4.7531638888566 | | 2010 | 3.9110619553403 | | 2009 | 2.9208971180536 | | 2008 | 11.270665238085 | | 2007 | 4.7439063902165 | | 2006 | 3.5449859160503 | | 2005 | 3.4936853461953 | | 2004 | 3.6322800495662 | | 2003 | 2.7125924747435 | | 2002 | 1.8329938900205 | | 2001 | 1.7722043735102 | | 2000 | 1.8537903532528 | | 1999 | 2.669373690537 | | 1998 | 3.417319489758 | | 1997 | 3.6011610326095 | | 1996 | 4.6813062391641 | | 1995 | 6.5437906852417 | | 1994 | 5.1125989044431 | | 1993 | 9.3703441597146 | | 1992 | 9.3597515895313 | | 1991 | 9 | | 1990 | 8.4514624080388 | | 1989 | 7.7408860396134 | | 1988 | 5.9115449637349 | | 1987 | 4.2224166624075 | | 1986 | 7.4333333333332 | | 1985 | 7.2543617998164 | | 1984 | 8.116397955171 | | 1983 | 5.4936655143209 | | 1982 | 8.3312557558116 | | 1981 | 10.758503416015 | | 1980 | 9.6260566461318 | | 1978 | 9.7160327495434 | | 1977 | 11.989283322105 | | 1976 | 10.317415887741 | | 1975 | 9.6696954815125 | | 1974 | 15.528281750267 | | 1973 | 8.2666666660001 |
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