| Year | Value | | 2021 | 1.7534351388402 | | 2020 | 1.7534351388402 | | 2019 | 1.7534351388402 | | 2018 | 1.7534351388402 | | 2017 | 1.7534351388402 | | 2016 | 1.7534351388402 | | 2015 | 1.7534351388402 | | 2014 | 1.7534351388402 | | 2013 | 1.7534351388402 | | 2012 | 1.5940319444002 | | 2011 | 1.5940319444002 | | 2010 | 1.7534351388402 | | 2009 | 1.7534351388402 | | 2008 | 1.7534351388402 | | 2007 | 1.5940319444002 | | 2006 | 1.6737335416202 | | 2005 | 1.7534351388402 | | 2004 | 1.8012560971722 | | 2003 | 1.7263365957854 | | 2002 | 1.6960499888418 | | 2001 | 1.6657633818982 | | 2000 | 1.6625753180094 | | 1999 | 1.6625753180094 | | 1998 | 1.6625753180094 | | 1997 | 1.6625753180094 | | 1996 | 1.6561991902318 | | 1995 | 1.6498230624542 | | 1994 | 1.6418529027322 | | 1993 | 1.6322887110658 | | 1992 | 1.6306946791214 | | 1991 | 1.629100647177 | | 1990 | 1.629100647177 | | 1989 | 1.6275066152326 | | 1988 | 1.6275066152326 | | 1987 | 1.6227245193994 | | 1986 | 1.6163483916218 | | 1985 | 1.6083782318998 | | 1984 | 1.6004080721778 | | 1983 | 1.5924379124558 | | 1982 | 1.5844677527338 | | 1981 | 1.5764975930118 | | 1980 | 1.5685274332898 | | 1979 | 1.5605572735678 | | 1978 | 1.5525871138458 | | 1977 | 1.5446169541238 | | 1976 | 1.5382408263462 | | 1975 | 1.5302706666242 | | 1974 | 1.5223005069022 | | 1973 | 1.5159243791246 | | 1972 | 1.5079542194026 | | 1971 | 1.4999840596806 | | 1970 | 1.4920138999586 | | 1969 | 1.4840437402366 | | 1968 | 1.4760735805145 | | 1967 | 1.4681034207926 | | 1966 | 1.4601332610705 | | 1965 | 1.4521631013486 | | 1964 | 1.4441929416265 | | 1963 | 1.4362227819046 | | 1962 | 1.4282526221826 | | 1961 | 1.4202824624605 |
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