Year | Value | 2015 | 7.3087434548228 | 2014 | 9.2144655010721 | 2013 | 13.943431510191 | 2012 | 15.691729089205 | 2011 | 18.554976759716 | 2010 | 22.209200898213 | 2009 | 22.124983702631 | 2008 | 25.264071370047 | 2007 | 28.585606884949 | 2006 | 27.972123426392 | 2005 | 29.659179283594 | 2004 | 28.695570693339 | 2003 | 27.726180617665 | 2002 | 26.60412855113 | 2001 | 24.30053716669 | 2000 | 26.659419586712 | 1999 | 24.457411175977 | 1998 | 21.569894149477 | 1997 | 21.509824949493 | 1996 | 20.583534817836 | 1995 | 19.740846424214 | 1994 | 18.796003762123 | 1993 | 20.287092675434 | 1992 | 16.338529620164 | 1991 | 14.942707646395 | 1990 | 13.709630913392 | 1989 | 16.995504302287 | 1988 | 15.668952653384 | 1987 | 13.854979134533 | 1986 | 12.048646532188 | 1985 | 11.537193753526 | 1984 | 9.5135388013199 | 1983 | 12.770581008697 | 1982 | 9.0486557098649 | 1981 | 11.801346091942 | 1980 | 13.931369608503 | 1979 | 18.574108962876 | 1978 | 21.923561632031 | 1977 | 20.808509530375 | 1976 | 19.694418966796 | 1975 | 14.871245806015 | 1974 | 15.55117446646 | 1973 | 15.821800434044 | 1972 | 12.131812562424 | 1971 | 9.5153745189833 | 1970 | 6.521609932803 | 1969 | 7.7093384261002 | 1968 | 5.5440506390218 | 1967 | 4.2527986738519 | 1966 | 7.1579224786409 | 1965 | 7.2205762141031 | 1964 | 6.5036408374399 | 1963 | 6.2388760797291 | 1962 | 5.8259528305926 | 1961 | 5.5788579679717 | 1960 | 5.3408161874835 |
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