| Year | Value | | 2018 | 1.5172708908432 | | 2017 | 1.5033877955479 | | 2016 | 1.3600606727573 | | 2015 | 1.1672451790582 | | 2014 | 1.0098722688096 | | 2013 | 0.90829254022104 | | 2012 | 0.90201012497029 | | 2011 | 0.96913368594481 | | 2010 | 1.0506521737083 | | 2009 | 1.1124856911286 | | 2008 | 1.1761571000216 | | 2007 | 1.2344964589158 | | 2006 | 1.2887374453095 | | 2005 | 1.3497447087134 | | 2004 | 1.4171784504644 | | 2003 | 1.4777216360431 | | 2002 | 1.526919519402 | | 2001 | 1.5672641591134 | | 2000 | 1.603751779784 | | 1999 | 1.6420507675797 | | 1998 | 1.6836379256431 | | 1997 | 1.7310897024548 | | 1996 | 1.7822740658207 | | 1995 | 1.8356158876533 | | 1994 | 1.884887437034 | | 1993 | 1.9240099235985 | | 1992 | 1.9485015801455 | | 1991 | 1.9616335116685 | | 1990 | 1.967956347636 | | 1989 | 1.9757138072939 | | 1988 | 1.990330759353 | | 1987 | 2.0170872296101 | | 1986 | 2.0530768555767 | | 1985 | 2.0916332483872 | | 1984 | 2.1261665775667 | | 1983 | 2.1557118324185 | | 1982 | 2.1771328417339 | | 1981 | 2.1917882083548 | | 1980 | 2.2082211226644 | | 1979 | 2.2262517855784 | | 1978 | 2.2364308360101 | | 1977 | 2.2359874081981 | | 1976 | 2.2296614841151 | | 1975 | 2.2147035138772 | | 1974 | 2.2072930612719 | | 1973 | 2.2314561832673 | | 1972 | 2.3021696802827 | | 1971 | 2.40980503803 | | 1970 | 2.5346809654037 | | 1969 | 2.6552505462612 | | 1968 | 2.7651390642022 | | 1967 | 2.8519786333887 | | 1966 | 2.9182190184455 | | 1965 | 2.9815411245001 | | 1964 | 3.0456396927213 | | 1963 | 3.0936579580437 | | 1962 | 3.1202509181562 | | 1961 | 3.1271736575449 | | 1960 | 3.1189847066556 |
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