Year Years 1800 446.7 1950 118.4 1951 117.2 1952 115.8 1953 114.5 1954 113 1955 111.4 1956 109.7 1957 108 1958 106.2 1959 104.4 1960 102.6 1961 100.5 1962 98.3 1963 95.9 1964 93.3 1965 90.4 1966 87.2 1967 83.8 1968 80 1969 75.9 1970 71.8 1971 67.6 1972 63.3 1973 59 1974 54.7 1975 50.2 1976 45.8 1977 41.4 1978 37.4 1979 33.7 1980 30.5 1981 27.7 1982 25.4 1983 23.5 1984 21.9 1985 20.5 1986 19.5 1987 18.6 1988 17.8 1989 17.1 1990 16.5 1991 15.9 1992 15.5 1993 15 1994 14.7 1995 14.5 1996 14.3 1997 14.2 1998 14.2 1999 14.2 2000 14.2 2001 14.3 2002 14.3 2003 14.3 2004 14.3 2005 14.2 2006 14.2 2007 14.2 2008 14.2 2009 14.2 2010 14.3 2011 14.3 2012 14.3 2013 14.2