Year | Value | 2021 | 14.324141973665 | 2020 | 14.457874107729 | 2019 | 14.655383782933 | 2018 | 14.914909411556 | 2017 | 14.779676974741 | 2016 | 15.362087836934 | 2015 | 16.140616588642 | 2014 | 15.808339070115 | 2013 | 17.012524796726 | 2012 | 15.440935674025 | 2011 | 16.361834793709 | 2010 | 14.932647554229 | 2009 | 14.194230839514 | 2008 | 15.384886404341 | 2007 | 15.14315655684 | 2006 | 15.636992711511 | 2005 | 16.061860265693 | 2004 | 14.853330905937 | 2003 | 14.481568803232 | 2002 | 13.470312762099 | 2001 | 13.070218321755 | 2000 | 12.97673290176 | 1999 | 12.889215599899 | 1998 | 13.788167441694 | 1997 | 16.105479257204 | 1996 | 16.726217629269 | 1995 | 16.440930820127 | 1994 | 16.035689018159 | 1993 | 15.399276711039 | 1992 | 15.5917839861 | 1991 | 17.413503976745 | 1990 | 16.90732301092 | 1989 | 15.580572884684 | 1988 | 14.80673226173 | 1987 | 13.649990606198 | 1986 | 13.616146658207 | 1985 | 13.687836896425 | 1984 | 14.10679378036 | 1983 | 14.139582436161 | 1982 | 12.640555768317 | 1981 | 13.476976361436 | 1980 | 13.143149674711 | 1979 | 12.374128052045 | 1978 | 11.661408976639 | 1977 | 11.608921720183 | 1976 | 10.783838200218 | 1975 | 11.193867996803 | 1974 | 12.583810613319 | 1973 | 10.173345491094 | 1972 | 11.041152347757 |
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