| Year | Value | | 2022 | 50.115025711625 | | 2021 | 50.137257855209 | | 2020 | 50.162530139902 | | 2019 | 50.180891406084 | | 2018 | 50.193170852617 | | 2017 | 50.204303468566 | | 2016 | 50.215244977897 | | 2015 | 50.221593857053 | | 2014 | 50.222387087664 | | 2013 | 50.222876937004 | | 2012 | 50.222548362567 | | 2011 | 50.221013131876 | | 2010 | 50.219984904534 | | 2009 | 50.218771658328 | | 2008 | 50.217177366426 | | 2007 | 50.215263442489 | | 2006 | 50.213479075037 | | 2005 | 50.213441704558 | | 2004 | 50.214105966626 | | 2003 | 50.214550651182 | | 2002 | 50.214276672753 | | 2001 | 50.212806174888 | | 2000 | 50.208473212605 | | 1999 | 50.200787167036 | | 1998 | 50.193882269611 | | 1997 | 50.187642597731 | | 1996 | 50.184015179533 | | 1995 | 50.184938398707 | | 1994 | 50.185933784543 | | 1993 | 50.187245047861 | | 1992 | 50.188112566946 | | 1991 | 50.181926843731 | | 1990 | 50.169790988765 | | 1989 | 50.15530286496 | | 1988 | 50.14139707579 | | 1987 | 50.128794857904 | | 1986 | 50.117317749076 | | 1985 | 50.118773292097 | | 1984 | 50.130383903857 | | 1983 | 50.14046111861 | | 1982 | 50.147834983958 | | 1981 | 50.153207541504 | | 1980 | 50.154839327755 | | 1979 | 50.153251426207 | | 1978 | 50.151768734487 | | 1977 | 50.148936951992 | | 1976 | 50.14833341501 | | 1975 | 50.146199985235 | | 1974 | 50.13801402684 | | 1973 | 50.126330470684 | | 1972 | 50.112086640833 | | 1971 | 50.097010704194 | | 1970 | 50.089604744181 | | 1969 | 50.085684411751 | | 1968 | 50.0771031765 | | 1967 | 50.070556062379 | | 1966 | 50.06529358545 | | 1965 | 50.062244738032 | | 1964 | 50.06276171644 | | 1963 | 50.0583198923 | | 1962 | 50.052950698689 | | 1961 | 50.059989972246 | | 1960 | 50.080954880273 |
|