| Year | Value | | 2022 | 2.0166679021273 | | 2021 | 1.5183493670661 | | 2020 | 1.6663586742327 | | 2019 | 1.9628449198635 | | 2018 | 1.9288375139876 | | 2017 | 2.4309764177611 | | 2016 | 2.1553119879921 | | 2015 | 2.3599511813687 | | 2014 | 2.3569787048404 | | 2013 | 2.3111762527522 | | 2012 | 2.4015418998288 | | 2011 | 2.2226605032672 | | 2010 | 1.8254058035237 | | 2009 | 1.8517752304365 | | 2008 | 1.7874966322579 | | 2007 | 1.5443868465055 | | 2006 | 1.5950519177449 | | 2005 | 1.5300546634087 | | 2004 | 1.4213325647131 | | 2003 | 1.2152008796464 | | 2002 | 1.0476608159644 | | 2001 | 1.1904563452871 | | 2000 | 1.3440829957314 | | 1999 | 1.3506212853024 | | 1998 | 1.2438708026922 | | 1997 | 1.2535024836943 | | 1996 | 1.3611439410986 | | 1995 | 1.4047424635593 | | 1994 | 1.3618401374009 | | 1993 | 1.3423870292469 | | 1992 | 1.3283475712522 | | 1991 | 1.3396831695389 | | 1990 | 1.2517457070082 | | 1989 | 0.97262774612358 | | 1988 | 0.72561457850343 | | 1987 | 0.64808339349221 | | 1986 | 0.44867099908019 | | 1985 | 0.19325681867559 | | 1984 | 0.1027856081308 | | 1983 | 0.0265336520752 | | 1982 | 0.082107428492381 | | 1981 | 0.29477313546538 | | 1980 | 0.35598093179143 | | 1979 | 0.23425126906217 | | 1978 | 0.1794391971245 | | 1977 | 0.17366284698414 | | 1976 | 0.49494251918095 | | 1975 | 1.0924478394389 | | 1974 | 1.3040581681769 | | 1973 | 1.1046665664828 | | 1972 | 1.2130403118934 | | 1971 | 0.95365691827723 | | 1970 | 0.49388946672146 | | 1969 | 0.4900878599711 | | 1968 | 0.2549025372326 | | 1967 | 0.32890340463349 | | 1966 | 0.71987626682955 | | 1965 | 1.1376686982108 | | 1964 | 1.1199012496307 | | 1963 | 1.0390106651756 | | 1962 | 1.224930818843 | | 1961 | 0.91152553647068 |
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