| Year | Value | | 2022 | 50.540193744919 | | 2021 | 50.579544258499 | | 2020 | 50.633280339163 | | 2019 | 50.680808896392 | | 2018 | 50.724783774521 | | 2017 | 50.770688779827 | | 2016 | 50.824586684654 | | 2015 | 50.885748851045 | | 2014 | 50.946793940795 | | 2013 | 51.01134596156 | | 2012 | 51.073681712866 | | 2011 | 51.128599723064 | | 2010 | 51.183630033687 | | 2009 | 51.239004828488 | | 2008 | 51.292780815375 | | 2007 | 51.349855128731 | | 2006 | 51.398867228566 | | 2005 | 51.428834944293 | | 2004 | 51.453962834853 | | 2003 | 51.480205036231 | | 2002 | 51.522939603376 | | 2001 | 51.585381632549 | | 2000 | 51.656059331997 | | 1999 | 51.729796087043 | | 1998 | 51.801697943857 | | 1997 | 51.877959805218 | | 1996 | 51.9395039734 | | 1995 | 51.980591585078 | | 1994 | 52.024753823315 | | 1993 | 52.070947727903 | | 1992 | 52.118422190956 | | 1991 | 52.166688327361 | | 1990 | 52.215889980056 | | 1989 | 52.264354628675 | | 1988 | 52.294537523545 | | 1987 | 52.30676230341 | | 1986 | 52.321068076339 | | 1985 | 52.338227297444 | | 1984 | 52.356043812041 | | 1983 | 52.380447045944 | | 1982 | 52.430553563951 | | 1981 | 52.506927503967 | | 1980 | 52.587856300163 | | 1979 | 52.673070010028 | | 1978 | 52.765293180266 | | 1977 | 52.705577590314 | | 1976 | 52.500069273186 | | 1975 | 52.308110388821 | | 1974 | 52.111208800952 | | 1973 | 51.907428772262 | | 1972 | 51.69978727947 | | 1971 | 51.569921708651 | | 1970 | 51.524713506544 | | 1969 | 51.491612699138 | | 1968 | 51.46860659917 | | 1967 | 51.44865323836 | | 1966 | 51.432817434323 | | 1965 | 51.420840342947 | | 1964 | 51.408731826204 | | 1963 | 51.415243086894 | | 1962 | 51.453905479329 | | 1961 | 51.501938541894 | | 1960 | 51.549186220551 |
|