| Year | Value | | 2023 | 48.743123594852 | | 2022 | 48.797845480015 | | 2021 | 48.853251644715 | | 2020 | 48.910761660252 | | 2019 | 48.968709340899 | | 2018 | 49.023761154262 | | 2017 | 49.074804988919 | | 2016 | 49.123059703168 | | 2015 | 49.169512478559 | | 2014 | 49.214253708113 | | 2013 | 49.256610143745 | | 2012 | 49.296888773906 | | 2011 | 49.334755001246 | | 2010 | 49.368331885208 | | 2009 | 49.390956514489 | | 2008 | 49.404862449373 | | 2007 | 49.418633260685 | | 2006 | 49.433533720347 | | 2005 | 49.44980657302 | | 2004 | 49.467246600664 | | 2003 | 49.485817126385 | | 2002 | 49.505761459905 | | 2001 | 49.526926783606 | | 2000 | 49.553041151372 | | 1999 | 49.599245856806 | | 1998 | 49.662950039685 | | 1997 | 49.727214269595 | | 1996 | 49.789431963715 | | 1995 | 49.848591071219 | | 1994 | 49.902770048651 | | 1993 | 49.953296740767 | | 1992 | 50.008020685514 | | 1991 | 50.065903470674 | | 1990 | 50.125150879195 | | 1989 | 50.164501799524 | | 1988 | 50.179230179125 | | 1987 | 50.192245259093 | | 1986 | 50.203935946175 | | 1985 | 50.215944651077 | | 1984 | 50.229939356911 | | 1983 | 50.246874914039 | | 1982 | 50.26695363557 | | 1981 | 50.289686570656 | | 1980 | 50.314062287069 | | 1979 | 50.338011605281 | | 1978 | 50.359656731868 | | 1977 | 50.378147685876 | | 1976 | 50.393261929444 | | 1975 | 50.405489691562 | | 1974 | 50.415423004058 |
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