| Year | Value | | 2022 | 6.8028011534161 | | 2021 | 3.3951931852753 | | 2020 | 0.71699963230783 | | 2019 | 1.9492690241159 | | 2018 | 2.268225672481 | | 2017 | 1.5968841285298 | | 2016 | 1.4287595470109 | | 2015 | 1.1252413609428 | | 2014 | 1.9066359071786 | | 2013 | 0.93829189781532 | | 2012 | 1.5156782312452 | | 2011 | 2.9121350887235 | | 2010 | 1.7768715409263 | | 2009 | 0.2994668030093 | | 2008 | 2.370270674443 | | 2007 | 2.1383839926684 | | 2006 | 2.0020253953416 | | 2005 | 2.2135520343977 | | 2004 | 1.8572587185726 | | 2003 | 2.7585632136011 | | 2002 | 2.2583944094086 | | 2001 | 2.5251201397991 | | 2000 | 2.7194399569198 | | 1999 | 1.7348429510592 | | 1998 | 0.99594245665802 | | 1997 | 1.6212163808453 | | 1996 | 1.5705311250714 | | 1995 | 2.1487603305785 | | 1994 | 0.16556291390729 | | 1993 | 1.8650793650794 | | 1992 | 1.4901329037455 | | 1991 | 5.62586408593 | | 1990 | 4.780476933363 | | 1989 | 4.9836218998596 | | 1988 | 4.0282341487161 | | 1987 | 4.3561087122174 | | 1986 | 4.1947862908562 | | 1985 | 3.9620305406521 | | 1984 | 4.3047783039174 | | 1983 | 5.8635880297737 | | 1982 | 10.768971899714 | | 1981 | 12.471612414837 | | 1980 | 10.129220508545 | | 1979 | 9.1446769790718 | | 1978 | 8.9737233515121 | | 1977 | 7.9764453961457 | | 1976 | 7.5417386298215 | | 1975 | 10.672188595094 | | 1974 | 10.997171145686 | | 1973 | 7.4876472824021 | | 1972 | 4.9880287310455 | | 1971 | 2.7049180327868 | | 1970 | 3.3460398136383 | | 1969 | 4.5615589016829 | | 1968 | 4.0552995391705 | | 1967 | 3.5799522673031 | | 1966 | 3.8156590683845 | | 1965 | 2.3326572008113 | | 1964 | 1.9121447028424 | | 1963 | 1.6281512605043 | | 1962 | 1.0615711252653 | | 1961 | 1.0187667560321 | | 1960 | 1.3586956521739 |
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