| Year | Value | | 2022 | 50.25781222759 | | 2021 | 50.253467038145 | | 2020 | 50.231265990858 | | 2019 | 50.217652098981 | | 2018 | 50.230405225303 | | 2017 | 50.252048430018 | | 2016 | 50.281200459759 | | 2015 | 50.324326614516 | | 2014 | 50.363762026178 | | 2013 | 50.390967674994 | | 2012 | 50.421343136911 | | 2011 | 50.453576680219 | | 2010 | 50.47527391128 | | 2009 | 50.495548579469 | | 2008 | 50.5325888339 | | 2007 | 50.577803640301 | | 2006 | 50.620540079146 | | 2005 | 50.652348665706 | | 2004 | 50.667814339631 | | 2003 | 50.67354211396 | | 2002 | 50.676705178715 | | 2001 | 50.67888883097 | | 2000 | 50.686874696185 | | 1999 | 50.699329975134 | | 1998 | 50.709487920759 | | 1997 | 50.718484359095 | | 1996 | 50.72706170452 | | 1995 | 50.735502362321 | | 1994 | 50.745240043196 | | 1993 | 50.75789544118 | | 1992 | 50.772414589184 | | 1991 | 50.790431791655 | | 1990 | 50.807161895352 | | 1989 | 50.824377844399 | | 1988 | 50.844833271572 | | 1987 | 50.863830638798 | | 1986 | 50.883327914883 | | 1985 | 50.901859053388 | | 1984 | 50.91666295053 | | 1983 | 50.929724150301 | | 1982 | 50.94217433932 | | 1981 | 50.953020403669 | | 1980 | 50.96693552954 | | 1979 | 50.979705241001 | | 1978 | 50.986641207789 | | 1977 | 50.992455357634 | | 1976 | 50.999795298151 | | 1975 | 51.007862032297 | | 1974 | 51.01789635779 | | 1973 | 51.02940366511 | | 1972 | 51.042676114139 | | 1971 | 51.06202625882 | | 1970 | 51.086186591103 | | 1969 | 51.102918727242 | | 1968 | 51.108142208301 | | 1967 | 51.102026483621 | | 1966 | 51.086562852413 | | 1965 | 51.075541620017 | | 1964 | 51.07695351028 | | 1963 | 51.085262955417 | | 1962 | 51.093579052413 | | 1961 | 51.10154650532 | | 1960 | 51.11058781565 |
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