| Year | Value | | 2022 | 1.9387234180687 | | 2021 | 1.9153614542139 | | 2020 | 2.0028401160111 | | 2019 | 1.8364614707329 | | 2018 | 1.8430087230024 | | 2017 | 1.9086420123444 | | 2016 | 1.9172823680414 | | 2015 | 1.8722582812768 | | 2014 | 1.8629614394727 | | 2013 | 1.8498759182869 | | 2012 | 1.8710805998476 | | 2011 | 1.8914062136109 | | 2010 | 1.9694193527524 | | 2009 | 2.0981473345273 | | 2008 | 1.8970758958191 | | 2007 | 1.9075286335775 | | 2006 | 1.9750982998737 | | 2005 | 2.0237069189264 | | 2004 | 2.1043508352725 | | 2003 | 2.0956804128006 | | 2002 | 2.0462579903799 | | 2001 | 2.0306952899655 | | 2000 | 2.0850182448033 | | 1999 | 2.1778429702217 | | 1998 | 2.2262083065277 | | 1997 | 2.3754096531413 | | 1996 | 2.4144739505933 | | 1995 | 2.4924961893684 | | 1994 | 2.6603749603516 | | 1993 | 2.6895348064364 | | 1992 | 2.6906607106318 | | 1991 | 2.8121364380672 | | 1990 | 2.8052676270668 | | 1989 | 2.8799353124635 | | 1988 | 2.9631806088489 | | 1987 | 3.1204516051352 | | 1986 | 3.0857650157535 | | 1985 | 3.1439328022973 | | 1984 | 3.1873692509231 | | 1983 | 3.2371317747523 | | 1982 | 3.2238391338373 | | 1981 | 3.2461326104642 | | 1980 | 3.1552050849191 | | 1979 | 3.1393954430751 | | 1978 | 3.1514873141178 | | 1977 | 3.2315686103442 | | 1976 | 3.1561395842335 | | 1975 | 3.1971454640285 | | 1974 | 3.0864405807862 | | 1973 | 3.143719204797 | | 1972 | 3.2303045904313 | | 1971 | 3.3160930482422 | | 1970 | 3.4585577173323 | | 1969 | 3.6797517267577 | | 1968 | 4.1368460377768 | | 1967 | 4.295245946919 | | 1966 | 4.2901032742439 | | 1965 | 4.3953195137661 | | 1964 | 4.5402502666987 | | 1963 | 4.7400857174986 | | 1962 | 5.1588713495319 | | 1961 | 5.2956075387672 | | 1960 | 5.4284858849305 |
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