| Year | Value | | 2021 | 7.1848215875277 | | 2020 | 7.1848215875277 | | 2019 | 7.1848215875277 | | 2018 | 7.1848215875277 | | 2017 | 7.1848215875277 | | 2016 | 7.1848215875277 | | 2015 | 7.1848215875277 | | 2014 | 7.1848215875277 | | 2013 | 7.1848215875277 | | 2012 | 7.1848215875277 | | 2011 | 7.1848215875277 | | 2010 | 7.1848215875277 | | 2009 | 6.9940741117526 | | 2008 | 6.8669091279025 | | 2007 | 6.6125791602024 | | 2006 | 6.2310842086523 | | 2005 | 6.3582491925023 | | 2004 | 5.8495892571022 | | 2003 | 5.7224242732521 | | 2002 | 5.6588417813271 | | 2001 | 5.0865993540019 | | 2000 | 4.9594343701518 | | 1999 | 5.0230168620769 | | 1998 | 5.0865993540019 | | 1997 | 4.9594343701518 | | 1996 | 4.7686868943768 | | 1995 | 4.6415219105267 | | 1994 | 4.5397899234467 | | 1993 | 4.4762074315217 | | 1992 | 4.4762074315217 | | 1991 | 4.4507744347516 | | 1990 | 4.3871919428266 | | 1989 | 4.3236094509016 | | 1988 | 4.2600269589766 | | 1987 | 4.1964444670515 | | 1986 | 4.0692794832015 | | 1985 | 4.0056969912765 | | 1984 | 3.9421144993515 | | 1983 | 3.8149495155014 | | 1982 | 3.8149495155014 | | 1981 | 3.7132175284214 | | 1980 | 3.6496350364963 | | 1979 | 3.6496350364963 | | 1978 | 3.6496350364963 | | 1977 | 3.6496350364963 | | 1976 | 3.6496350364963 | | 1975 | 3.6496350364963 | | 1974 | 3.6242020397263 | | 1973 | 3.6242020397263 | | 1972 | 3.5606195478013 | | 1971 | 3.5415448002238 | | 1970 | 3.5415448002238 | | 1969 | 3.4334545639513 | | 1968 | 3.3062895801012 | | 1967 | 3.1791245962512 | | 1966 | 3.1460617004502 | | 1965 | 3.1409751010962 | | 1964 | 3.1282586027112 | | 1963 | 3.1219003535187 | | 1962 | 3.1155421043261 | | 1961 | 3.1079122052951 |
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