Year Years 1800 381.4 1931 285.5 1972 152.7 1973 147.5 1974 142.8 1975 138.6 1976 135.2 1977 132.7 1978 131 1979 130.2 1980 129.7 1981 129.5 1982 128.9 1983 127.3 1984 125 1985 121.6 1986 117.5 1987 113.2 1988 109.6 1989 107.8 1990 108.2 1991 110.9 1992 115.5 1993 119.6 1994 121.2 1995 119.7 1996 116.2 1997 111.5 1998 105.9 1999 99.9 2000 93.5 2001 87.1 2002 80.8 2003 74.9 2004 69.8 2005 65.4 2006 61.8 2007 58.9 2008 56.6 2009 54.5 2010 52.7 2011 51 2012 49.3 2013 47.7