| Year | Value | | 2022 | 1.6376655408969 | | 2021 | 1.7218868704434 | | 2020 | 1.9659836923944 | | 2019 | 1.8437353781843 | | 2018 | 1.7152973747833 | | 2017 | 1.7051532859499 | | 2016 | 1.6173438359967 | | 2015 | 1.4981232726649 | | 2014 | 1.4622794277647 | | 2013 | 1.4052521813978 | | 2012 | 1.3931899961181 | | 2011 | 1.4425275514079 | | 2010 | 1.5076279549281 | | 2009 | 1.5969097991894 | | 2008 | 1.3703337166088 | | 2007 | 1.4591720779909 | | 2006 | 1.4446680279441 | | 2005 | 1.5758846731433 | | 2004 | 1.8487851441738 | | 2003 | 1.9748544868435 | | 2002 | 2.0805919313208 | | 2001 | 1.7045414598759 | | 2000 | 1.7058318732318 | | 1999 | 2.0391055714536 | | 1998 | 2.1567376666965 | | 1997 | 2.0160795707442 | | 1996 | 2.1630749742096 | | 1995 | 2.3074910395754 | | 1994 | 2.7331370824311 | | 1993 | 2.687349844566 | | 1992 | 2.964700275299 | | 1991 | 2.7474871958821 | | 1990 | 2.8862268942944 | | 1989 | 2.9101570921425 | | 1988 | 2.8930898629137 | | 1987 | 2.9783244255997 | | 1986 | 2.80841701831 | | 1985 | 2.7960002317027 | | 1984 | 2.5444343506659 | | 1983 | 2.7949715316534 | | 1982 | 2.7445921064168 | | 1981 | 2.62397215286 | | 1980 | 2.6190188688838 | | 1979 | 2.7665459136892 | | 1978 | 2.841318929137 | | 1977 | 3.0981768059645 | | 1976 | 3.1240297816753 | | 1975 | 3.2084302833856 | | 1974 | 3.0355353426347 | | 1973 | 3.1336051210528 | | 1972 | 3.2914659675223 | | 1971 | 3.3915044049155 | | 1970 | 3.472839490717 | | 1969 | 3.6042524993517 | | 1968 | 3.6078431372549 | | 1967 | 3.5125628140704 | | 1966 | 3.5679598306731 | | 1965 | 3.3979365193093 | | 1964 | 3.119163984583 | | 1963 | 3.2084273230985 | | 1962 | 3.2415179099184 | | 1961 | 3.004204357243 | | 1960 | 3.2004355980398 |
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