| Year | Value | | 2022 | 48.192593764822 | | 2021 | 48.152037471617 | | 2020 | 48.111274869218 | | 2019 | 48.072075787272 | | 2018 | 48.034013823314 | | 2017 | 47.9958309925 | | 2016 | 47.957531097913 | | 2015 | 47.918897403754 | | 2014 | 48.052454450934 | | 2013 | 48.421313367679 | | 2012 | 48.6303885695 | | 2011 | 48.604665554615 | | 2010 | 48.577487665298 | | 2009 | 48.549139420983 | | 2008 | 48.519487709172 | | 2007 | 48.488821351559 | | 2006 | 48.45633677818 | | 2005 | 48.421652489886 | | 2004 | 48.389539266972 | | 2003 | 48.34244698549 | | 2002 | 48.27075259898 | | 2001 | 48.182406247155 | | 2000 | 48.080920474651 | | 1999 | 47.968994753347 | | 1998 | 47.850891017944 | | 1997 | 47.733922869489 | | 1996 | 47.645939961933 | | 1995 | 47.628289027286 | | 1994 | 47.710070156231 | | 1993 | 47.891423413406 | | 1992 | 48.139187930757 | | 1991 | 48.407952369354 | | 1990 | 48.670267400298 | | 1989 | 48.797265078283 | | 1988 | 48.788553825142 | | 1987 | 48.781766905696 | | 1986 | 48.776529195267 | | 1985 | 48.774301360862 | | 1984 | 48.77223388071 | | 1983 | 48.768463307996 | | 1982 | 48.765661173836 | | 1981 | 48.76385935478 | | 1980 | 48.76293640272 | | 1979 | 48.762860849791 | | 1978 | 48.764151052823 | | 1977 | 48.768436306047 | | 1976 | 48.776618250297 | | 1975 | 48.787524461528 | | 1974 | 48.799398550217 | | 1973 | 48.812615493597 | | 1972 | 48.827214191568 | | 1971 | 48.840813532805 | | 1970 | 48.847868270563 | | 1969 | 48.851631310913 | | 1968 | 48.857785934011 | | 1967 | 48.861797610771 | | 1966 | 48.862351526727 | | 1965 | 48.86042100681 | | 1964 | 48.856230578165 | | 1963 | 48.848005379075 | | 1962 | 48.837756723357 | | 1961 | 48.826930149532 | | 1960 | 48.81394350517 |
|