| Year | Value | | 2022 | 1.7447594596952 | | 2021 | 1.7961013366299 | | 2020 | 1.6173999431383 | | 2019 | 1.5392735463293 | | 2018 | 1.4159496009361 | | 2017 | 0.93597164915614 | | 2016 | 0.7540645812946 | | 2015 | 0.49767257206961 | | 2014 | 0.81749247375079 | | 2013 | 1.3367506209925 | | 2012 | 1.3939805606183 | | 2011 | 1.8833036053339 | | 2010 | 2.0489466497019 | | 2009 | 2.5654369568839 | | 2008 | 2.6843051783046 | | 2007 | 1.5871131924468 | | 2006 | 1.6934046708008 | | 2005 | 2.4520824365458 | | 2004 | 4.0529646475642 | | 2003 | 4.0755415244098 | | 2002 | 3.4138275867775 | | 2001 | 2.844671522323 | | 2000 | 1.5329954312569 | | 1999 | 1.4414586985436 | | 1998 | 1.3519875380381 | | 1997 | 1.2067841093189 | | 1996 | 4.8345047921831 | | 1995 | 5.4645807963518 | | 1994 | 3.0361293061836 | | 1993 | 3.0887728057642 | | 1992 | -5.9641855166882 | | 1991 | -5.2881855515915 | | 1990 | 2.2497645204013 | | 1989 | 2.435793684501 | | 1988 | 2.5268990457633 | | 1987 | 2.569479931273 | | 1986 | 2.6174479766947 | | 1985 | 2.6489230182985 | | 1984 | 2.7282829316494 | | 1983 | 2.7470573655815 | | 1982 | 2.7358158124778 | | 1981 | 2.7253394248323 | | 1980 | 2.6991583921127 | | 1979 | 2.6774412864828 | | 1978 | 2.6696888149444 | | 1977 | 2.6593094446221 | | 1976 | 2.6383912041561 | | 1975 | 2.6290520096203 | | 1974 | 2.6315119465002 | | 1973 | 2.6260877583367 | | 1972 | 2.6146603780719 | | 1971 | 2.5969845453576 | | 1970 | 2.5613839650959 | | 1969 | 2.5273122866686 | | 1968 | 2.515497895223 | | 1967 | 2.51449196822 | | 1966 | 2.5111321527142 | | 1965 | 2.5001065231618 | | 1964 | 2.4751684279368 | | 1963 | 2.4415501747353 | | 1962 | 2.3921656953536 | | 1961 | 2.3243025948184 |
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