| Year | Value | | 2022 | 48.010425683645 | | 2021 | 47.933950346589 | | 2020 | 47.920332476871 | | 2019 | 47.878537374296 | | 2018 | 47.809398960226 | | 2017 | 47.745471139319 | | 2016 | 47.704629517935 | | 2015 | 47.667774657399 | | 2014 | 47.629237463975 | | 2013 | 47.602626028095 | | 2012 | 47.578679450485 | | 2011 | 47.53500993897 | | 2010 | 47.501633402007 | | 2009 | 47.492486196092 | | 2008 | 47.483645948375 | | 2007 | 47.482295891356 | | 2006 | 47.485274776543 | | 2005 | 47.48202838629 | | 2004 | 47.48449476363 | | 2003 | 47.503385529759 | | 2002 | 47.528788032716 | | 2001 | 47.557195920005 | | 2000 | 47.588088870331 | | 1999 | 47.623842453209 | | 1998 | 47.663792311193 | | 1997 | 47.703792063557 | | 1996 | 47.738703314534 | | 1995 | 47.779454369344 | | 1994 | 47.828866976574 | | 1993 | 47.881398274725 | | 1992 | 47.933522081839 | | 1991 | 47.97928084415 | | 1990 | 48.020241733101 | | 1989 | 48.064940344842 | | 1988 | 48.107605087661 | | 1987 | 48.145243682607 | | 1986 | 48.184236246513 | | 1985 | 48.225093746852 | | 1984 | 48.272321859773 | | 1983 | 48.321032782993 | | 1982 | 48.361466207892 | | 1981 | 48.399109789507 | | 1980 | 48.436409766103 | | 1979 | 48.455953422494 | | 1978 | 48.459698775286 | | 1977 | 48.463010057663 | | 1976 | 48.461219672944 | | 1975 | 48.455638404344 | | 1974 | 48.451976281769 | | 1973 | 48.451295556374 | | 1972 | 48.45115705822 | | 1971 | 48.455501420733 | | 1970 | 48.462749649406 | | 1969 | 48.455183048619 | | 1968 | 48.434403472435 | | 1967 | 48.412258619869 | | 1966 | 48.388051820609 | | 1965 | 48.364688848167 | | 1964 | 48.343730293744 | | 1963 | 48.32258241749 | | 1962 | 48.300405529906 | | 1961 | 48.27471434583 | | 1960 | 48.244096483785 |
|