Year | Value | 2018 | 11.720602412022 | 2017 | 11.100497895543 | 2016 | 10.890459893014 | 2015 | 10.460842800621 | 2014 | 9.8864596603428 | 2013 | 10.804020162867 | 2012 | 10.658054041178 | 2011 | 10.087558987885 | 2010 | 10.225454436553 | 2009 | 9.7319353122857 | 2008 | 10.741386208675 | 2007 | 11.681698863997 | 2006 | 10.858923790361 | 2005 | 9.9577696898702 | 2004 | 9.4913777796196 | 2003 | 9.0516901433539 | 2002 | 8.6941318826845 | 2001 | 8.1876964518347 | 2000 | 8.8658641886264 | 1999 | 9.3107998475988 | 1998 | 8.8139386922035 | 1997 | 9.6184925118874 | 1996 | 9.5069779101626 | 1995 | 9.5335094504417 | 1994 | 9.2643630552992 | 1993 | 8.8401528037125 | 1992 | 10.064157623365 | 1991 | 10.425313656644 | 1990 | 10.2848743778 | 1989 | 10.8174857128 | 1988 | 10.659078205491 | 1987 | 10.411415391457 | 1986 | 10.750048276106 | 1985 | 10.313611191573 | 1984 | 9.7285924175974 | 1983 | 9.6476146463498 | 1982 | 9.6351268402498 | 1981 | 9.6724128392482 | 1980 | 9.4828009527044 | 1979 | 9.9670075211042 | 1978 | 9.5421715215673 | 1977 | 8.8568407294559 | 1976 | 9.3801346231057 | 1975 | 9.2305228798812 | 1974 | 8.5588104693405 |
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