| Year | Value | | 2022 | 49.34460170824 | | 2021 | 49.344951054338 | | 2020 | 49.338301004638 | | 2019 | 49.326233481318 | | 2018 | 49.30908701908 | | 2017 | 49.288399724038 | | 2016 | 49.264007281592 | | 2015 | 49.238212408367 | | 2014 | 49.208812188596 | | 2013 | 49.173907461357 | | 2012 | 49.139729114097 | | 2011 | 49.104145056146 | | 2010 | 49.056379143807 | | 2009 | 48.981404010951 | | 2008 | 48.888443336736 | | 2007 | 48.784779770285 | | 2006 | 48.676944296432 | | 2005 | 48.571397689728 | | 2004 | 48.476900332855 | | 2003 | 48.393634123281 | | 2002 | 48.313646344497 | | 2001 | 48.229968237721 | | 2000 | 48.151910963513 | | 1999 | 48.107499263608 | | 1998 | 48.086856877032 | | 1997 | 48.076907916606 | | 1996 | 48.077632725789 | | 1995 | 48.100277114531 | | 1994 | 48.13248800833 | | 1993 | 48.172735864717 | | 1992 | 48.220826056678 | | 1991 | 48.268757202937 | | 1990 | 48.314783472785 | | 1989 | 48.360232403696 | | 1988 | 48.401750676039 | | 1987 | 48.436101384249 | | 1986 | 48.455884348307 | | 1985 | 48.469613691812 | | 1984 | 48.492001938326 | | 1983 | 48.508822823463 | | 1982 | 48.505619442249 | | 1981 | 48.505336430927 | | 1980 | 48.533136798266 | | 1979 | 48.580272990074 | | 1978 | 48.636882564773 | | 1977 | 48.699136222477 | | 1976 | 48.76521554935 | | 1975 | 48.834686709189 | | 1974 | 48.908716113758 | | 1973 | 48.988940940483 | | 1972 | 49.076583352879 | | 1971 | 49.171791571618 | | 1970 | 49.273566324923 | | 1969 | 49.344038132179 | | 1968 | 49.368691788613 | | 1967 | 49.382767947406 | | 1966 | 49.397910887105 | | 1965 | 49.414383284527 | | 1964 | 49.433606077063 | | 1963 | 49.453558202951 | | 1962 | 49.472126211889 | | 1961 | 49.491326316195 | | 1960 | 49.511064521403 |
|