| Year | Value | | 2022 | 1.4294693103718 | | 2021 | 1.317260691189 | | 2020 | 1.3533282546044 | | 2019 | 1.2433039672391 | | 2018 | 1.1801424443564 | | 2017 | 1.7774097701393 | | 2016 | 1.4434381383767 | | 2015 | 1.7468929247271 | | 2014 | 1.8126934433304 | | 2013 | 1.9911753862629 | | 2012 | 1.8907065308424 | | 2010 | 3.1655338455733 | | 2009 | 3.4223768015911 | | 2008 | 3.1997448448176 | | 2007 | 3.3623707999217 | | 2006 | 3.4105394876342 | | 2005 | 3.6128365460508 | | 2004 | 4.2042695829224 | | 2003 | 4.3298520503222 | | 2002 | 4.2897057364113 | | 2001 | 4.3703970926002 | | 2000 | 4.1954654674687 | | 1999 | 4.8289979650556 | | 1998 | 4.5134741965034 | | 1997 | 4.0671432138721 | | 1996 | 4.1001279328663 | | 1995 | 4.573870054136 | | 1994 | 5.8413548207308 | | 1993 | 5.3469223733996 | | 1992 | 5.8580214886021 | | 1991 | 5.998974627201 | | 1990 | 5.4536688155256 | | 1988 | 5.170968459916 | | 1987 | 6.6237004653207 | | 1986 | 7.9365228701924 | | 1985 | 8.1777948651943 | | 1984 | 8.4477247980502 | | 1983 | 7.7578086182518 | | 1982 | 7.8348052799868 | | 1981 | 6.7447051490348 | | 1980 | 7.0148112592141 | | 1979 | 6.2787377919572 | | 1978 | 5.5838371166099 | | 1977 | 5.145279502659 | | 1976 | 5.406175811805 | | 1975 | 5.3535108888203 | | 1974 | 4.655362247484 | | 1973 | 4.6433599261555 | | 1972 | 4.6568710177255 | | 1971 | 4.0623371574334 | | 1970 | 4.0152573313192 | | 1969 | 4.4877387428199 | | 1968 | 4.3255057861612 | | 1967 | 3.4132626504568 | | 1966 | 3.2520701816923 | | 1965 | 3.687626326353 | | 1964 | 3.4910212059842 | | 1962 | 4.2830438493667 |
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