Year | Value | 2021 | 21.654026908805 | 2020 | 21.654026908805 | 2019 | 21.644455363097 | 2018 | 22.18078097432 | 2017 | 22.298127331264 | 2016 | 22.330217909486 | 2015 | 22.345819651991 | 2014 | 20.453392304968 | 2013 | 20.519647255545 | 2012 | 20.421620828375 | 2011 | 20.548767252716 | 2010 | 20.547472980651 | 2009 | 20.143112014887 | 2008 | 20.085232358884 | 2007 | 20.186973297756 | 2006 | 20.294442046708 | 2005 | 20.323682940317 | 2004 | 20.864643467604 | 2003 | 21.224239687812 | 2002 | 21.252616325874 | 2001 | 21.373236041017 | 2000 | 19.93184594612 | 1999 | 18.433746044425 | 1998 | 17.70561307567 | 1997 | 17.413745429967 | 1996 | 17.063504255123 | 1995 | 16.599588313005 | 1994 | 16.786998064457 | 1993 | 16.946757196842 | 1992 | 16.916034286768 | 1991 | 16.492058127746 | 1990 | 16.402961688531 | 1989 | 16.590371439983 | 1988 | 16.774708900427 | 1987 | 16.980552397923 | 1986 | 17.112660911241 | 1985 | 17.253986297582 | 1984 | 17.880733663093 | 1983 | 17.972902393315 | 1982 | 18.065071123537 | 1981 | 18.157239853759 | 1980 | 18.249408583981 | 1979 | 18.341577314203 | 1978 | 18.430673753418 | 1977 | 18.372300224277 | 1976 | 18.126516943685 | 1975 | 17.512058742204 | 1974 | 17.512058742204 | 1973 | 17.450612922056 | 1972 | 17.358444191834 | 1971 | 17.296998371686 | 1970 | 17.296998371686 | 1969 | 17.204829641464 | 1968 | 17.17410673139 | 1967 | 17.112660911241 | 1966 | 17.051215091093 | 1965 | 17.051215091093 | 1964 | 17.051215091093 | 1963 | 17.051215091093 | 1962 | 17.051215091093 | 1961 | 17.051215091093 |
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