| Year | Value | | 2022 | 6.1537562193304 | | 2021 | 1.4978921793472 | | 2020 | 0.63854495677671 | | 2019 | 1.6420600176894 | | 2018 | 1.1578236245152 | | 2017 | 1.3643544815071 | | 2016 | 0.6427027715273 | | 2015 | 1.1005482637893 | | 2014 | 0.31030647218167 | | 2013 | 1.1802843636655 | | 2012 | 2.3758205776039 | | 2011 | 2.9629852819288 | | 2010 | 1.5156351361853 | | 2009 | 2.0843274608234 | | 2008 | 4.2586217189707 | | 2007 | 1.2492192379763 | | 2006 | 2.7737800648147 | | 2005 | 3.0079665245031 | | 2004 | 2.7908284806775 | | 2003 | 1.303837774426 | | 2002 | 2.1884904806055 | | 2001 | 2.929492443241 | | 2000 | 2.3695928753181 | | 1999 | 2.1347688880639 | | 1998 | 2.3852513541766 | | 1997 | 3.1120779195327 | | 1996 | 2.0540000000001 | | 1995 | 4.4266455028665 | | 1994 | 4.1299218163826 | | 1993 | 4.1448195418049 | | 1992 | 1.6332120988904 | | 1991 | 2.5421928478697 | | 1990 | 2.9834058606356 | | 1989 | 0.84769135922621 | | 1988 | 0.93834438712851 | | 1987 | 0.43172566942244 | | 1986 | 2.0278887141476 | | 1985 | 0.23520745967747 | | 1984 | 0.44250000075008 | | 1983 | 0.88099756031751 | | 1982 | 5.8182339721866 | | 1981 | 11.509755837712 | | 1980 | 15.747254103486 | | 1979 | 7.1471074379789 | | 1978 | 4.7075112495149 | | 1977 | 10.040374800236 | | 1976 | 0.55151283025858 | | 1975 | 8.7916666661669 | | 1974 | 7.2556162720401 | | 1973 | 7.6892899178615 | | 1972 | 3.3727610678115 | | 1971 | 2.3238121583881 | | 1970 | 3.7156588480926 | | 1969 | 2.3342876018622 | | 1968 | 2.0373005768228 | | 1967 | 0.69386831571305 | | 1966 | 0.52312357869953 | | 1965 | 1.6022184561013 | | 1964 | 2.1802439985969 | | 1963 | 1.8763531392127 | | 1962 | 0.16867469895764 | | 1961 | 2.511321531007 | | 1960 | 3.3846153846155 |
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