| Year | Value | | 2022 | 1.6790923384616 | | 2021 | 1.7200628309881 | | 2020 | 1.7396316667744 | | 2019 | 1.3115096247263 | | 2018 | 1.3592910114542 | | 2017 | 1.3573704810149 | | 2016 | 1.3348352516956 | | 2015 | 1.2082282526571 | | 2014 | 1.2829696542767 | | 2013 | 1.3990212868043 | | 2012 | 1.4269248887623 | | 2011 | 1.4759565970898 | | 2010 | 1.5004945759252 | | 2009 | 1.5542107022709 | | 2008 | 1.5356747965256 | | 2007 | 1.44705251877 | | 2006 | 1.5213433256469 | | 2005 | 1.6009687639927 | | 2004 | 1.6826732696168 | | 2003 | 1.7089955372423 | | 2002 | 1.7061872461629 | | 2001 | 1.6793647376815 | | 2000 | 1.7410595043212 | | 1999 | 1.6832997980888 | | 1998 | 1.644508879132 | | 1997 | 1.6266927994662 | | 1996 | 1.5884922793504 | | 1995 | 1.4678431433464 | | 1994 | 1.713742759551 | | 1993 | 1.7867679733127 | | 1992 | 1.7519769834749 | | 1991 | 1.8588526837555 | | 1990 | 1.8807984132592 | | 1989 | 2.0264273198954 | | 1988 | 2.0728574592448 | | 1987 | 2.0603536440041 | | 1986 | 1.9771426421067 | | 1985 | 1.9363689201664 | | 1984 | 2.0086077736065 | | 1983 | 2.0165014199205 | | 1982 | 2.0053729031431 | | 1981 | 1.8211125060357 | | 1980 | 1.7636432370897 | | 1979 | 1.8739594666397 | | 1978 | 1.8797551045682 | | 1977 | 1.8908085121882 | | 1976 | 1.8281436688527 | | 1975 | 1.9752321680362 | | 1974 | 2.0706267739896 | | 1973 | 2.1958174142776 | | 1972 | 2.3911760162955 | | 1971 | 2.2389709472173 | | 1970 | 2.0582100542783 | | 1969 | 2.4224008269415 | | 1968 | 2.6489615918823 | | 1967 | 2.767746940336 | | 1966 | 2.9887199805542 | | 1965 | 2.7475801622298 | | 1964 | 2.7273558982661 | | 1963 | 2.7534379536088 | | 1962 | 2.6338383568595 | | 1961 | 2.573869075305 | | 1960 | 2.7138259882858 |
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