| Year | Value | | 2022 | 1.7216829026165 | | 2021 | 1.2615298982188 | | 2020 | 1.4258227677934 | | 2019 | 1.3537176162563 | | 2018 | 1.3625343739024 | | 2017 | 1.351297608053 | | 2016 | 1.4196526264493 | | 2015 | 1.4499609716867 | | 2014 | 1.4519301874846 | | 2013 | 1.5338609345099 | | 2012 | 1.5265846585454 | | 2011 | 1.4894089839291 | | 2010 | 1.4917581596003 | | 2009 | 1.5607423559336 | | 2008 | 1.3909394042854 | | 2007 | 1.2875205062467 | | 2006 | 1.4424018624366 | | 2005 | 1.4645177398114 | | 2004 | 1.4701635645735 | | 2003 | 1.4468572626493 | | 2002 | 1.1546372286549 | | 2001 | 1.1445128325845 | | 2000 | 1.2411475036878 | | 1999 | 1.223103771578 | | 1998 | 1.4631755578076 | | 1997 | 1.5351550506601 | | 1996 | 1.530472271213 | | 1995 | 1.4225414992492 | | 1994 | 1.7556035954033 | | 1993 | 1.8680115065657 | | 1992 | 1.9071310116086 | | 1991 | 1.7812310364932 | | 1990 | 1.5633514986376 | | 1989 | 1.5343144923525 | | 1988 | 1.6076911731184 | | 1987 | 1.6455330096053 | | 1986 | 1.72390995339 | | 1985 | 1.6765790727635 | | 1984 | 1.6040418011372 | | 1983 | 1.8232638142335 | | 1982 | 1.6437501499772 | | 1981 | 1.5455867305725 | | 1980 | 1.6709354799366 | | 1979 | 1.4790093096785 | | 1978 | 1.4294441050702 | | 1977 | 1.4053520114942 | | 1976 | 1.340124616754 | | 1975 | 1.5081598199212 | | 1974 | 1.2701786674789 | | 1973 | 1.453702040083 | | 1972 | 1.530845543649 | | 1971 | 1.4490468749276 | | 1970 | 1.3758540167931 | | 1969 | 1.437477698063 | | 1968 | 1.755074400253 | | 1967 | 1.6155211526962 | | 1966 | 1.7139513137864 | | 1965 | 1.7973403827777 | | 1964 | 1.8592730316521 | | 1963 | 1.9271417869506 | | 1962 | 2.5131783086401 | | 1961 | 1.8361815196588 | | 1960 | 1.7690410476246 |
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