| Year | Value | | 2022 | 50.587800016063 | | 2021 | 50.595557219013 | | 2020 | 50.609751245509 | | 2019 | 50.634053525314 | | 2018 | 50.662310911092 | | 2017 | 50.696296753532 | | 2016 | 50.740944082483 | | 2015 | 50.785871092065 | | 2014 | 50.816890783383 | | 2013 | 50.844844298597 | | 2012 | 50.874634895368 | | 2011 | 50.902180816256 | | 2010 | 50.930430328805 | | 2009 | 50.956232796978 | | 2008 | 50.98732438104 | | 2007 | 51.022644742393 | | 2006 | 51.045933815156 | | 2005 | 51.064234548103 | | 2004 | 51.082344565688 | | 2003 | 51.104500700078 | | 2002 | 51.134908383578 | | 2001 | 51.16653771529 | | 2000 | 51.196039418037 | | 1999 | 51.223184785338 | | 1998 | 51.245143148094 | | 1997 | 51.266346727969 | | 1996 | 51.291212511596 | | 1995 | 51.316743354419 | | 1994 | 51.341989470354 | | 1993 | 51.372427888103 | | 1992 | 51.405807198994 | | 1991 | 51.44178510184 | | 1990 | 51.479491311118 | | 1989 | 51.513845874942 | | 1988 | 51.539160236779 | | 1987 | 51.554932346291 | | 1986 | 51.570522543742 | | 1985 | 51.582573041558 | | 1984 | 51.59121281967 | | 1983 | 51.60329037861 | | 1982 | 51.62149894103 | | 1981 | 51.641514917607 | | 1980 | 51.651288922626 | | 1979 | 51.648145225338 | | 1978 | 51.64129702887 | | 1977 | 51.654205897392 | | 1976 | 51.662590217623 | | 1975 | 51.650497265338 | | 1974 | 51.648518220363 | | 1973 | 51.660399565725 | | 1972 | 51.688498999209 | | 1971 | 51.71580062891 | | 1970 | 51.696568916783 | | 1969 | 51.668055316185 | | 1968 | 51.673381542142 | | 1967 | 51.68398483387 | | 1966 | 51.694829986641 | | 1965 | 51.712566076682 | | 1964 | 51.734115417493 | | 1963 | 51.754957731555 | | 1962 | 51.778004047931 | | 1961 | 51.805894346983 | | 1960 | 51.839894288553 |
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