| Year | Value | | 2022 | 1.0498012565365 | | 2021 | 1.1743551132072 | | 2020 | 1.3011022301943 | | 2019 | 1.2154310302692 | | 2018 | 1.2745312091978 | | 2017 | 1.2658702676188 | | 2016 | 1.2446561657601 | | 2015 | 1.2550980410008 | | 2014 | 1.2764556719407 | | 2013 | 1.3227743682965 | | 2012 | 1.3108068761063 | | 2011 | 1.2896073931191 | | 2010 | 1.3633141767456 | | 2009 | 1.4040568623966 | | 2008 | 1.289126684052 | | 2007 | 1.2425458900862 | | 2006 | 1.1968577490752 | | 2005 | 1.213513260527 | | 2004 | 1.1374872593393 | | 2003 | 1.1479030393371 | | 2002 | 1.2232948035676 | | 2001 | 1.3026557973214 | | 2000 | 1.2723227829926 | | 1999 | 1.3111957813557 | | 1998 | 1.391639798447 | | 1997 | 1.3608323567522 | | 1996 | 1.5030990386834 | | 1995 | 1.5832466872201 | | 1994 | 1.451323170703 | | 1993 | 1.3851380189248 | | 1992 | 1.3169513187065 | | 1991 | 1.4813407822744 | | 1990 | 1.7370943629486 | | 1989 | 2.0642476295326 | | 1988 | 1.6482211967333 | | 1987 | 1.8945393121777 | | 1986 | 1.9079333102198 | | 1985 | 1.7362425005785 | | 1984 | 1.9213982172827 | | 1983 | 2.201330800185 | | 1982 | 1.8837191857148 | | 1981 | 1.5455385231916 | | 1980 | 1.4768573478569 | | 1979 | 1.6029661096918 | | 1978 | 1.6443208723466 | | 1977 | 1.7332095755287 | | 1976 | 1.4800464585321 | | 1975 | 1.5739366068901 | | 1974 | 1.897162592192 | | 1973 | 1.9765829832974 | | 1972 | 1.9636521873115 | | 1971 | 2.0295699387043 | | 1970 | 1.6109471220671 | | 1969 | 1.4008808319695 | | 1968 | 1.4700114347709 | | 1967 | 1.6328033949713 | | 1966 | 1.6502899905267 | | 1965 | 1.7318690882137 | | 1964 | 1.7336072582768 | | 1963 | 1.8872955060497 | | 1962 | 1.8532716526194 | | 1961 | 1.5779444746093 | | 1960 | 1.9009666476022 |
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