| Year | Value | | 2022 | 1.3074631185262 | | 2021 | 1.1932765614962 | | 2020 | 1.1460864242763 | | 2019 | 1.0934092255277 | | 2018 | 1.0322460921077 | | 2017 | 1.023179204574 | | 2016 | 1.0530163887864 | | 2015 | 1.0665020525904 | | 2014 | 1.1264473180005 | | 2013 | 1.1125205386496 | | 2012 | 1.1301102886762 | | 2011 | 1.1016911643403 | | 2010 | 1.1871285413707 | | 2009 | 1.1598043438116 | | 2008 | 1.1637472367963 | | 2007 | 1.2999815075726 | | 2006 | 1.3182055234573 | | 2005 | 1.4069875148622 | | 2004 | 1.4412833599289 | | 2003 | 1.5967899694361 | | 2002 | 1.6411545404721 | | 2001 | 1.7127473730764 | | 2000 | 1.8326730498249 | | 1999 | 1.8908850725378 | | 1998 | 1.8726237875703 | | 1997 | 1.9532769236896 | | 1996 | 2.140907755181 | | 1995 | 2.1589688166556 | | 1994 | 2.2799385244374 | | 1993 | 2.3868343480419 | | 1992 | 2.4441930717023 | | 1991 | 2.4543063902538 | | 1990 | 2.5689803154592 | | 1989 | 2.5088339222615 | | 1988 | 2.5852867488074 | | 1987 | 2.6532905146666 | | 1986 | 2.5865682563945 | | 1985 | 2.6730084000738 | | 1984 | 2.671961322623 | | 1983 | 2.7378226181065 | | 1982 | 2.8537547840746 | | 1981 | 2.9482371468705 | | 1980 | 2.9234515960268 | | 1979 | 3.123357422665 | | 1978 | 3.1477754879379 | | 1977 | 3.101082115368 | | 1976 | 3.0031129022302 | | 1975 | 3.0816031384544 | | 1974 | 3.2153970491202 | | 1973 | 3.2785873055075 | | 1972 | 3.407964349866 | | 1971 | 3.4100367854362 | | 1970 | 3.3586682614704 | | 1969 | 3.4592807325458 | | 1968 | 3.4765468776781 | | 1967 | 3.6114518498327 | | 1966 | 3.858013271171 | | 1965 | 3.912630749391 | | 1964 | 3.8661977381093 | | 1963 | 3.9672772424099 | | 1962 | 3.8634442931593 | | 1961 | 3.7206133312957 | | 1960 | 3.7769709399814 |
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