| Year | Value | | 2021 | 47.368376347599 | | 2020 | 48.126612876882 | | 2019 | 47.443729378328 | | 2018 | 47.39850409903 | | 2017 | 47.232110780888 | | 2016 | 46.944707534537 | | 2015 | 46.934909696594 | | 2014 | 47.1080048336 | | 2013 | 47.059207733255 | | 2012 | 47.446280451963 | | 2011 | 48.261110929693 | | 2010 | 47.175786861695 | | 2009 | 50.995820817553 | | 2008 | 50.933725106105 | | 2007 | 50.49947767041 | | 2006 | 52.092582919822 | | 2005 | 51.924395260014 | | 2004 | 53.29873012764 | | 2003 | 52.798458725183 | | 2002 | 55.173201867511 | | 2001 | 58.075679911195 | | 2000 | 60.116229716935 | | 1999 | 60.188057070097 | | 1998 | 60.21417610761 | | 1997 | 60.259884423259 | | 1996 | 60.315387377975 | | 1995 | 60.798589571974 | | 1994 | 61.076104345555 | | 1993 | 61.102223383068 | | 1992 | 61.193640014365 | | 1991 | 61.226288811257 | | 1990 | 61.356883998825 | | 1989 | 61.402592314473 | | 1988 | 61.445035750433 | | 1987 | 61.605014855203 | | 1986 | 61.637663652094 | | 1985 | 61.751934441216 | | 1984 | 61.833556433445 | | 1983 | 61.637663652094 | | 1982 | 61.676842208365 | | 1981 | 61.738874922459 | | 1980 | 62.05556825231 | | 1979 | 62.189428319566 | | 1978 | 62.395115739985 | | 1977 | 62.551829965066 | | 1976 | 62.682425152633 | | 1975 | 62.764047144863 | | 1974 | 62.871788174606 | | 1973 | 63.097064873159 | | 1972 | 63.243984459173 | | 1971 | 63.691272976591 | | 1970 | 63.805543765712 | | 1969 | 63.851252081361 | | 1968 | 64.569525612981 | | 1967 | 64.706650559927 | | 1966 | 65.124555160142 | | 1965 | 65.121290280453 | | 1964 | 65.722028143263 | | 1963 | 65.898331646479 | | 1962 | 66.152992262235 | | 1961 | 66.348885043586 |
|