Year | Value | 2021 | 19.573006579695 | 2020 | 18.936636378118 | 2019 | 19.245092021316 | 2018 | 19.318412380249 | 2017 | 19.160716626126 | 2016 | 18.964975731103 | 2015 | 19.060886809549 | 2014 | 19.324303475217 | 2013 | 19.335875908844 | 2012 | 19.113525025212 | 2011 | 19.510480989846 | 2010 | 19.286945961151 | 2009 | 19.00311776668 | 2008 | 20.010960362649 | 2007 | 20.232104135053 | 2006 | 20.068695158314 | 2005 | 19.772509766559 | 2004 | 19.131418667909 | 2003 | 19.159963347896 | 2002 | 19.359774569234 | 2001 | 19.8608022211 | 2000 | 20.170389111274 | 1999 | 19.862715233372 | 1998 | 20.112024061553 | 1997 | 19.838033735363 | 1996 | 19.416631713135 | 1995 | 19.292884046006 | 1994 | 18.678965048728 | 1993 | 18.366101153353 | 1992 | 18.689743710966 | 1991 | 18.802084935959 | 1990 | 18.099898615521 | 1989 | 17.714197370517 | 1988 | 17.710430121246 | 1987 | 17.721414968965 | 1986 | 17.821431424254 | 1985 | 17.519514844906 | 1984 | 17.223578988737 | 1983 | 17.242044395307 | 1982 | 17.335871630252 | 1981 | 16.955404545236 | 1980 | 16.871846648222 | 1979 | 16.615358675736 | 1978 | 16.726335990565 | 1977 | 16.865201464965 | 1976 | 16.77207048159 | 1975 | 16.162822010156 | 1974 | 16.3548515877 | 1973 | 15.930349780118 |
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