Year | Value | 2021 | 17.163380243921 | 2020 | 16.200074090409 | 2019 | 17.713008199022 | 2018 | 18.04038894707 | 2017 | 18.202537033096 | 2016 | 19.078526100896 | 2015 | 18.732390589402 | 2014 | 23.075000057809 | 2013 | 22.931262638248 | 2012 | 22.519822110088 | 2011 | 21.842518978675 | 2010 | 21.839986588558 | 2009 | 22.062376309002 | 2008 | 23.810941221499 | 2007 | 25.937168346525 | 2006 | 26.818812774603 | 2005 | 25.4571402375 | 2004 | 25.069723079588 | 2003 | 24.160739179046 | 2002 | 23.516845782921 | 2001 | 24.208238152221 | 2000 | 26.349940410777 | 1999 | 26.651059972965 | 1998 | 26.494328405031 | 1997 | 26.873585146346 | 1996 | 27.211037028131 | 1995 | 26.526589180102 | 1994 | 27.056503848906 | 1993 | 25.840533160926 | 1992 | 25.932385985911 | 1991 | 25.629226317111 | 1990 | 25.359919186493 | 1989 | 25.829153681814 | 1988 | 28.751259138882 | 1987 | 27.448050085686 | 1986 | 27.353541303976 | 1985 | 27.205578176372 | 1984 | 28.119450019491 | 1983 | 27.535257057305 | 1982 | 26.384423309563 | 1981 | 25.314227907079 | 1980 | 24.226882222745 | 1979 | 21.964239989756 | 1978 | 22.109371758325 | 1977 | 22.533029591428 | 1976 | 23.664943533801 | 1975 | 21.295618565842 | 1974 | 21.997264779486 | 1973 | 22.169296006196 | 1972 | 21.859989420365 |
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