| Year | Value | | 2021 | 70.552593930138 | | 2020 | 71.648650865258 | | 2019 | 72.348727128026 | | 2018 | 72.153551331523 | | 2017 | 71.864079877057 | | 2016 | 71.626167717551 | | 2015 | 71.351206105041 | | 2014 | 71.057847560141 | | 2013 | 70.722231772167 | | 2012 | 70.387099035504 | | 2011 | 70.043694320278 | | 2010 | 69.68114777107 | | 2009 | 69.386059730628 | | 2008 | 68.970064674081 | | 2007 | 68.804194372604 | | 2006 | 68.543566512906 | | 2005 | 68.16989304973 | | 2004 | 67.773537427821 | | 2003 | 67.546966371992 | | 2002 | 67.266825268874 | | 2001 | 66.94506391915 | | 2000 | 66.553234820318 | | 1999 | 66.259764530817 | | 1998 | 65.970650435218 | | 1997 | 65.582306743486 | | 1996 | 65.210559903024 | | 1995 | 64.919634049573 | | 1994 | 64.624494611339 | | 1993 | 64.385509225972 | | 1992 | 64.180385642301 | | 1991 | 63.853602722004 | | 1990 | 63.672526952484 | | 1989 | 63.454227722504 | | 1988 | 63.136373270909 | | 1987 | 62.860575702129 | | 1986 | 62.532357103213 | | 1985 | 62.082544608014 | | 1984 | 61.700150305187 | | 1983 | 61.30863396844 | | 1982 | 60.872294750407 | | 1981 | 60.437641476699 | | 1980 | 60.012161029332 | | 1979 | 59.553355009804 | | 1978 | 59.062865738955 | | 1977 | 58.583735947176 | | 1976 | 58.002389418864 | | 1975 | 57.452246890971 | | 1974 | 56.896718032687 | | 1973 | 56.396335783952 | | 1972 | 55.757097480276 | | 1971 | 54.615949027238 | | 1970 | 54.525611737243 | | 1969 | 54.161618444379 | | 1968 | 53.728974455355 | | 1967 | 53.038598307374 | | 1966 | 52.550876768408 | | 1965 | 51.836362572958 | | 1964 | 52.076675926178 | | 1963 | 51.534427527355 | | 1962 | 51.082822848056 | | 1961 | 47.656703657422 | | 1960 | 45.029518159019 |
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