| Year | Value | | 2022 | 0.63707753130368 | | 2021 | 0.64258617283745 | | 2020 | 0.65547178930258 | | 2019 | 0.70125258357376 | | 2018 | 0.787111572078 | | 2017 | 0.84469272038074 | | 2016 | 0.86897371062616 | | 2015 | 0.93496964965472 | | 2014 | 1.0193598434941 | | 2013 | 1.0681230405756 | | 2012 | 1.0894678320772 | | 2011 | 1.1016098327597 | | 2010 | 1.1171771715916 | | 2009 | 1.1447312759588 | | 2008 | 1.1846850301031 | | 2007 | 1.2331930305438 | | 2006 | 1.4869533865185 | | 2005 | 2.0303534399667 | | 2004 | 2.3921091909983 | | 2003 | 2.4854610625318 | | 2002 | 2.5877632951691 | | 2001 | 2.6927782942808 | | 2000 | 2.8005701842376 | | 1999 | 2.4549756895154 | | 1998 | 1.8619968242241 | | 1997 | 1.7284374081592 | | 1996 | 1.8700487681779 | | 1995 | 1.196815188577 | | 1994 | 0.080990467896011 | | 1993 | -4.7077353479978 | | 1992 | -3.9094318576723 | | 1991 | 1.6459961439629 | | 1990 | 2.5817399269497 | | 1989 | 2.8248528720984 | | 1988 | 2.8810987695454 | | 1987 | 2.9365192647225 | | 1986 | 2.9733433987595 | | 1985 | 3.0091524273218 | | 1984 | 3.0518521608433 | | 1983 | 3.080064547601 | | 1982 | 3.1144791087324 | | 1981 | 3.1722133087445 | | 1980 | 3.2288812907995 | | 1979 | 3.2844376292493 | | 1978 | 3.3146547076743 | | 1977 | 3.3137132103001 | | 1976 | 3.3085648998019 | | 1975 | 3.2976061489515 | | 1974 | 3.2932616672926 | | 1973 | 3.2894133902984 | | 1972 | 3.2778646596725 | | 1971 | 3.2724634140587 | | 1970 | 3.2638610076405 | | 1969 | 3.2296562861194 | | 1968 | 3.1784860910368 | | 1967 | 3.1306188376292 | | 1966 | 3.0760013185159 | | 1965 | 3.0118466294553 | | 1964 | 2.9429326781045 | | 1963 | 2.8928413467693 | | 1962 | 2.7563809624703 | | 1961 | 2.5897146250277 |
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