| Year | Value | | 2022 | 10.349568839127 | | 2021 | 5.8627824280106 | | 2020 | 5.226777792935 | | 2019 | 3.9051000086587 | | 2018 | 3.7366388215216 | | 2017 | 4.3783986499157 | | 2016 | 2.3510219748583 | | 2015 | 3.6915422885573 | | 2014 | 8.2740788623141 | | 2013 | 9.3415007656967 | | 2012 | 6.8739770867431 | | 2011 | 7.555856465809 | | 2010 | 12.61055199756 | | 2009 | 9.5922459893048 | | 2008 | 22.022838499184 | | 2007 | 9.2448206727558 | | 2006 | 8.5610640870617 | | 2005 | 15.05286588759 | | 2004 | 13.554502369668 | | 2003 | 10.086956521739 | | 2002 | 7.0763500931097 | | 2001 | 6.8019093078759 | | 2000 | 8.1710835612023 | | 1999 | 5.9542394911301 | | 1998 | 8.6318961301215 | | 1997 | 9.6575526126859 | | 1996 | 26.406656607404 | | 1995 | 19.908748836417 | | 1994 | 35.063394248477 | | 1993 | 22.069949418529 | | 1992 | 77.296592955965 | | 1991 | 51.071097730431 | | 1990 | 21.960175116508 | | 1989 | 14.329539032857 | | 1988 | 8.2667657440091 | | 1987 | 6.6524480496268 | | 1986 | 15.10537542098 | | 1985 | 25.673101239177 | | 1984 | 27.814769323745 | | 1983 | 11.582111084425 | | 1982 | 6.5454079672007 | | 1981 | 12.739718114509 | | 1980 | 27.308158988231 | | 1979 | 29.079259610979 | | 1978 | 34.899801524051 | | 1977 | 11.191001637036 | | 1976 | 9.7936532753465 | | 1975 | 17.37614678858 | | 1974 | 27.158189455022 | | 1973 | 17.682591982484 | | 1972 | 5.4277029963075 | | 1971 | 5.3361792958587 | | 1970 | 14.728004196257 | | 1969 | 6.303458534771 | | 1968 | 5.9286980500299 | | 1967 | 3.0235389610386 | | 1966 | 1.9023986765923 | | 1965 | 2.6315789473685 | | 1964 | 2.0134228187918 | | 1963 | 1.7625027539108 | | 1962 | 1.4075067024132 | | 1961 | 6.698450536352 | | 1960 | 3.274249138356 |
|