| Year | Value | | 2022 | 51.060075179796 | | 2021 | 51.012846367743 | | 2020 | 51.000063545021 | | 2019 | 50.991599792094 | | 2018 | 50.979355270829 | | 2017 | 50.960894212132 | | 2016 | 50.938208563517 | | 2015 | 50.905873527214 | | 2014 | 50.861757959541 | | 2013 | 50.809990924921 | | 2012 | 50.748688733253 | | 2011 | 50.679876144111 | | 2010 | 50.610438867612 | | 2009 | 50.538275261463 | | 2008 | 50.466554622638 | | 2007 | 50.401456323328 | | 2006 | 50.342195045548 | | 2005 | 50.28955909993 | | 2004 | 50.246183319597 | | 2003 | 50.214522549732 | | 2002 | 50.192955204275 | | 2001 | 50.180370951272 | | 2000 | 50.175496545649 | | 1999 | 50.180819078864 | | 1998 | 50.198533293417 | | 1997 | 50.225939155734 | | 1996 | 50.256946487192 | | 1995 | 50.293369818792 | | 1994 | 50.34035488047 | | 1993 | 50.394421666198 | | 1992 | 50.450966312757 | | 1991 | 50.506907200631 | | 1990 | 50.56191096027 | | 1989 | 50.614479328639 | | 1988 | 50.663688066757 | | 1987 | 50.713774988307 | | 1986 | 50.76628861458 | | 1985 | 50.821426237693 | | 1984 | 50.877183256262 | | 1983 | 50.934549616437 | | 1982 | 50.99745351337 | | 1981 | 51.062831126127 | | 1980 | 51.127907281586 | | 1979 | 51.191949949196 | | 1978 | 51.252610545569 | | 1977 | 51.307001174187 | | 1976 | 51.352837006272 | | 1975 | 51.391706126287 | | 1974 | 51.426549431647 | | 1973 | 51.450950164948 | | 1972 | 51.462485436654 | | 1971 | 51.467617773981 | | 1970 | 51.464884264518 | | 1969 | 51.452814861781 | | 1968 | 51.433840088735 | | 1967 | 51.409081426572 | | 1966 | 51.375121323189 | | 1965 | 51.33526399753 | | 1964 | 51.29687670257 | | 1963 | 51.257979590231 | | 1962 | 51.219211772192 | | 1961 | 51.182922262428 | | 1960 | 51.1467656377 |
|