| Year | Value | | 2022 | 1.2670953577821 | | 2021 | 0.12984747104576 | | 2020 | 0.47266709630267 | | 2019 | 2.2845890109214 | | 2018 | 2.3841500311734 | | 2017 | 2.2981605607971 | | 2016 | 2.014458627481 | | 2015 | 1.9246221367611 | | 2014 | 2.0220327110999 | | 2013 | 2.1217878838815 | | 2012 | 2.1997627566105 | | 2011 | 2.4815925615212 | | 2010 | 3.2064941063924 | | 2009 | 3.7430066096392 | | 2008 | 3.853874728353 | | 2007 | 3.9292048847208 | | 2006 | 3.9587966799178 | | 2005 | 3.0624298737648 | | 2004 | 2.1830904186556 | | 2003 | 2.3045935452553 | | 2002 | 2.4044722969764 | | 2001 | 2.4686013387817 | | 2000 | 2.5272363569949 | | 1999 | 2.589590212025 | | 1998 | 2.6440062797149 | | 1997 | 2.6843544407748 | | 1996 | 2.7230651153387 | | 1995 | 2.7987848534449 | | 1994 | 2.8779097679316 | | 1993 | 3.2177339939248 | | 1992 | 3.6960885052835 | | 1991 | 3.9780634831827 | | 1990 | 4.1560685488226 | | 1989 | 4.254562793708 | | 1988 | 4.3329062615322 | | 1987 | 4.3995472634998 | | 1986 | 4.49846930114 | | 1985 | 4.602955823483 | | 1984 | 4.692680571161 | | 1983 | 4.7497651098663 | | 1982 | 4.7811498570027 | | 1981 | 4.8594972618317 | | 1980 | 4.9341639432804 | | 1979 | 4.9917611909097 | | 1978 | 5.0701106474756 | | 1977 | 5.1041091678 | | 1976 | 5.2057062962587 | | 1975 | 5.3850426311308 | | 1974 | 5.4191249856403 | | 1973 | 5.2788266635573 | | 1972 | 4.9946215780396 | | 1971 | 4.6472491947296 | | 1970 | 4.3743440532261 | | 1969 | 4.1975256526707 | | 1968 | 4.0705415160731 | | 1967 | 3.938045753169 | | 1966 | 3.8285203038576 | | 1965 | 3.7612582198545 | | 1964 | 3.6847953487869 | | 1963 | 3.5936890817328 | | 1962 | 3.4795429120794 | | 1961 | 3.3169105563213 |
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