| Year | Value | | 2022 | 52.017442415007 | | 2021 | 52.014918154737 | | 2020 | 52.016146826414 | | 2019 | 52.024200341452 | | 2018 | 52.042358377199 | | 2017 | 52.064380675249 | | 2016 | 52.086516345423 | | 2015 | 52.109402083609 | | 2014 | 52.134771709607 | | 2013 | 52.164675294724 | | 2012 | 52.196366393304 | | 2011 | 52.22654865676 | | 2010 | 52.255630874244 | | 2009 | 52.279609795993 | | 2008 | 52.293869591997 | | 2007 | 52.301162739029 | | 2006 | 52.296201782772 | | 2005 | 52.278435876574 | | 2004 | 52.253881294389 | | 2003 | 52.231226820372 | | 2002 | 52.212459321848 | | 2001 | 52.196613187223 | | 2000 | 52.182828638191 | | 1999 | 52.173925328734 | | 1998 | 52.166980141829 | | 1997 | 52.159525707293 | | 1996 | 52.148535155136 | | 1995 | 52.132789823565 | | 1994 | 52.115634864072 | | 1993 | 52.104759578208 | | 1992 | 52.104647463013 | | 1991 | 52.119506297787 | | 1990 | 52.147276182336 | | 1989 | 52.189192533067 | | 1988 | 52.236776852824 | | 1987 | 52.284500937522 | | 1986 | 52.333103226183 | | 1985 | 52.379225983336 | | 1984 | 52.423580519056 | | 1983 | 52.469915967324 | | 1982 | 52.518059091969 | | 1981 | 52.564658301369 | | 1980 | 52.609164252221 | | 1979 | 52.646989355783 | | 1978 | 52.681366244231 | | 1977 | 52.721266879081 | | 1976 | 52.758366929793 | | 1975 | 52.805241128401 | | 1974 | 52.871977988406 | | 1973 | 52.94421564425 | | 1972 | 53.018469544451 | | 1971 | 53.091860090664 | | 1970 | 53.111835148408 | | 1969 | 53.11808437033 | | 1968 | 53.165208105863 | | 1967 | 53.216320901495 | | 1966 | 53.273135629738 | | 1965 | 53.339255452533 | | 1964 | 53.412130947917 | | 1963 | 53.495625095595 | | 1962 | 53.587681921929 | | 1961 | 53.684045313391 | | 1960 | 53.78618914907 |
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