| Year | Value | | 2024 | 0.67801082716061 | | 2023 | 0.7164674806165 | | 2022 | 0.756002474281 | | 2021 | 0.79659109175699 | | 2020 | 0.8382086166966 | | 2019 | 0.8808303327933 | | 2018 | 0.9244315237756 | | 2017 | 0.96898747340219 | | 2016 | 1.0144734654577 | | 2015 | 1.0617592318846 | | 2014 | 1.098372161174 | | 2013 | 1.1642378172099 | | 2012 | 1.2571989528032 | | 2011 | 1.3699389789091 | | 2010 | 1.4933767833335 | | 2009 | 1.6505114659045 | | 2008 | 1.8704806062678 | | 2007 | 2.1336874888265 | | 2006 | 2.4172621204938 | | 2005 | 2.6983345081829 | | 2004 | 2.9527420440959 | | 2003 | 3.1688817935991 | | 2002 | 3.3575502406095 | | 2001 | 3.5325692448276 | | 2000 | 3.7057281073362 | | 1999 | 3.8888161292177 | | 1998 | 4.0936226115547 | | 1997 | 4.3336498045005 | | 1996 | 4.6114880313576 | | 1995 | 4.9263137259117 | | 1994 | 5.2772894510374 | | 1993 | 5.6660937296162 | | 1992 | 6.0944050845294 | | 1991 | 6.5639020386584 | | 1990 | 7.0762631148847 | | 1989 | 7.6331668360896 | | 1988 | 8.2362917251546 | | 1987 | 8.8873163049611 | | 1986 | 9.576795945485 | | 1985 | 10.445456653898 | | 1984 | 11.671529445083 | | 1983 | 13.113041938516 | | 1982 | 14.596972370967 | | 1981 | 15.950298979205 | | 1980 | 17 | | 1979 | 17.776573587857 | | 1978 | 18.443474311675 | | 1977 | 19.027115029815 | | 1976 | 19.553908600635 |
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