| Year | Value | | 2022 | 7.6507917679853 | | 2021 | 5.5456543077348 | | 2020 | 5.6910747474621 | | 2019 | 3.6289496588548 | | 2018 | 3.3313951643766 | | 2017 | 4.5202286750887 | | 2016 | 4.1713902105348 | | 2015 | 4.1582558907216 | | 2014 | 6.8286478054436 | | 2013 | 7.6112812640637 | | 2012 | 9.4694033588846 | | 2011 | 10.250245033427 | | 2010 | 7.5815297762147 | | 2009 | 4.9768244765374 | | 2008 | 10.974644201788 | | 2007 | 7.1967289749047 | | 2006 | 6.7749288602821 | | 2005 | 6.9414754105746 | | 2004 | 4.1059369827296 | | 2003 | 3.8058589952885 | | 2002 | 3.3325649327191 | | 2001 | 3.1482614459062 | | 2000 | 4.0094359104519 | | 1999 | 4.6917056304844 | | 1998 | 9.3642430068323 | | 1997 | 7.1642521146271 | | 1996 | 8.9771523382646 | | 1995 | 9.4875483678937 | | 1994 | 8.3492867288339 | | 1993 | 9.9736647602921 | | 1992 | 11.787817041813 | | 1991 | 12.275172943889 | | 1990 | 8.9712325027328 | | 1989 | 7.8442647374004 | | 1988 | 8.9830033820899 | | 1987 | 8.801125812518 | | 1986 | 9.2259570019061 | | 1985 | 5.556424232365 | | 1984 | 7.0377066115702 | | 1983 | 12.377238078271 | | 1982 | 9.846772167797 | | 1981 | 11.879913592528 | | 1980 | 13.311366843543 | | 1979 | 7.2713651718995 | | 1978 | 6.7423919591302 | | 1977 | 9.1031614674232 | | 1976 | 0.89185852634482 | | 1975 | 7.1059888833697 | | 1974 | 23.234686440917 | | 1973 | 14.185294252517 | | 1972 | 6.3957917558592 | | 1971 | 2.8726594463327 | | 1970 | 5.6083984937449 | | 1969 | 3.6222892092762 | | 1968 | 2.2086411999877 | | 1967 | 4.500319483161 | | 1966 | 9.0147349734058 | | 1965 | 7.0202524039142 |
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