| Year | Value | | 2021 | 10.116803622823 | | 2020 | 10.01092845079 | | 2019 | 9.8341302166342 | | 2018 | 9.6616624516468 | | 2017 | 9.7267197288382 | | 2016 | 9.949853714551 | | 2015 | 10.062272643196 | | 2014 | 10.297553942528 | | 2013 | 10.469729777088 | | 2012 | 10.71737033558 | | 2011 | 10.999942972646 | | 2010 | 11.138511339234 | | 2009 | 11.321530172552 | | 2008 | 11.354588121055 | | 2007 | 11.231848588677 | | 2006 | 11.080040793499 | | 2005 | 10.970861550911 | | 2004 | 10.920301194345 | | 2003 | 10.934266318819 | | 2002 | 10.905977562905 | | 2001 | 11.113089205993 | | 2000 | 11.431048958749 | | 1999 | 11.794684105489 | | 1998 | 12.15579948825 | | 1997 | 12.406913318797 | | 1996 | 12.666377416059 | | 1995 | 12.892907497948 | | 1994 | 13.125938820491 | | 1993 | 13.254527693248 | | 1992 | 13.379245269733 | | 1991 | 13.309126358993 | | 1990 | 13.193362778359 | | 1989 | 13.064900738357 | | 1988 | 12.855224476463 | | 1987 | 12.629894909881 | | 1986 | 12.410242715566 | | 1985 | 12.229299363057 | | 1984 | 12.114654115653 | | 1983 | 11.980348560906 | | 1982 | 11.850571697502 | | 1981 | 11.788965839234 | | 1980 | 11.931178897362 | | 1979 | 12.029722330856 | | 1978 | 12.101796078861 | | 1977 | 12.242495585639 | | 1976 | 12.333532726758 | | 1975 | 12.326632012849 | | 1974 | 12.503386831997 | | 1973 | 12.846985096212 | | 1972 | 13.36868048124 | | 1971 | 13.997806191778 | | 1970 | 14.421130054627 | | 1969 | 14.672516766207 | | 1968 | 14.826421356786 | | 1967 | 15.038746487269 | | 1966 | 15.346722243274 | | 1965 | 15.77957363801 | | 1964 | 16.171344061411 | | 1963 | 16.306378436082 | | 1962 | 16.040474115078 | | 1961 | 15.577228396462 | | 1960 | 14.892019123331 |
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