| Year | Value | | 2022 | 8.0027998205212 | | 2021 | 4.6978588636374 | | 2020 | 1.2335843963063 | | 2019 | 1.8122100752602 | | 2018 | 2.4425832969282 | | 2017 | 2.1301100036596 | | 2016 | 1.2615832057054 | | 2015 | 0.11862713555245 | | 2014 | 1.6222229774082 | | 2013 | 1.4648326556272 | | 2012 | 2.0693372652607 | | 2011 | 3.156841568622 | | 2010 | 1.6400434423899 | | 2009 | 0.35554626629975 | | 2008 | 3.839100296651 | | 2007 | 2.8526724815014 | | 2006 | 3.225944100704 | | 2005 | 3.3927468454955 | | 2004 | 2.6772366930917 | | 2003 | 2.2700949733612 | | 2002 | 1.586031626506 | | 2001 | 2.8261711188541 | | 2000 | 3.3768572714993 | | 1999 | 2.1880271969736 | | 1998 | 1.5522790987436 | | 1997 | 2.3376899373074 | | 1996 | 2.9312041999344 | | 1995 | 2.8054196885366 | | 1994 | 2.6074415921545 | | 1993 | 2.9516569663856 | | 1992 | 3.0288196781497 | | 1991 | 4.2349639645385 | | 1990 | 5.3979564399032 | | 1989 | 4.8270030300894 | | 1988 | 4.0777411074441 | | 1987 | 3.6645632175169 | | 1986 | 1.8980477223428 | | 1985 | 3.5456441520936 | | 1984 | 4.3005354752343 | | 1983 | 3.2124352331607 | | 1982 | 6.1314270002749 | | 1981 | 10.334715340277 | | 1980 | 13.549201974968 | | 1979 | 11.254471129279 | | 1978 | 7.6309638388561 | | 1977 | 6.5016839947284 | | 1976 | 5.7448126354908 | | 1975 | 9.1431468649654 | | 1974 | 11.054804804805 | | 1973 | 6.1777600637704 | | 1972 | 3.2722782465528 | | 1971 | 4.2927666881305 | | 1970 | 5.8382553384825 | | 1969 | 5.4623862002875 | | 1968 | 4.2717961528854 | | 1967 | 2.7727856225931 | | 1966 | 3.0150753768844 | | 1965 | 1.5851692638366 | | 1964 | 1.2789115646259 | | 1963 | 1.2396694214875 | | 1962 | 1.1987733482019 | | 1961 | 1.0707241476472 | | 1960 | 1.4579759862779 |
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