| Year | Value | | 2021 | 82.762499547261 | | 2020 | 82.908302153195 | | 2019 | 83.673865056388 | | 2018 | 83.457147800935 | | 2017 | 83.369166470301 | | 2016 | 83.372169548965 | | 2015 | 83.200886123222 | | 2014 | 83.350208286027 | | 2013 | 83.104025434671 | | 2012 | 82.941484643748 | | 2011 | 82.876280860383 | | 2010 | 82.623197776867 | | 2009 | 82.468994620639 | | 2008 | 82.198889451011 | | 2007 | 82.081287701741 | | 2006 | 81.877212516788 | | 2005 | 81.573649790163 | | 2004 | 81.485418733636 | | 2003 | 81.063843210066 | | 2002 | 80.981211492736 | | 2001 | 80.852369809298 | | 2000 | 80.583530253287 | | 1999 | 80.340963038189 | | 1998 | 80.249383830621 | | 1997 | 80.094439608646 | | 1996 | 79.818907250105 | | 1995 | 79.538431379819 | | 1994 | 79.512299735282 | | 1993 | 79.218028884125 | | 1992 | 79.187799590982 | | 1991 | 78.936256347306 | | 1990 | 78.753435054691 | | 1989 | 78.56081108584 | | 1988 | 78.315597333583 | | 1987 | 78.210653417467 | | 1986 | 77.932969639567 | | 1985 | 77.720351370902 | | 1984 | 77.624513540047 | | 1983 | 77.324693322328 | | 1982 | 77.233310221095 | | 1981 | 76.92197855887 | | 1980 | 76.561989365184 | | 1979 | 76.571252175681 | | 1978 | 76.206735641338 | | 1977 | 76.035622591602 | | 1976 | 75.591483078003 | | 1975 | 75.321558767494 | | 1974 | 74.965630848513 | | 1973 | 74.576729676184 | | 1972 | 74.379641798682 | | 1971 | 74.125098212732 | | 1970 | 73.774493331566 | | 1969 | 73.491680326495 | | 1968 | 73.362516146482 | | 1967 | 73.37615855207 | | 1966 | 73.053777071344 | | 1965 | 72.719954476076 | | 1964 | 72.575296850574 | | 1963 | 72.031032637469 | | 1962 | 71.714128906993 | | 1961 | 71.695223685388 | | 1960 | 71.277352983187 |
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