Year	Years
1800	396.8
1900	381.9
1931	291.4
1950	173.4
1960	186.6
1970	122.4
1981	56.6
1982	55.1
1983	53
1984	50.9
1985	49.5
1986	48.8
1987	47.3
1988	43.9
1989	39.7
1990	36.6
1991	35
1992	33.5
1993	31
1994	27.8
1995	24.6
1996	21.8
1997	19.6
1998	18
1999	16.9
2000	16
2001	15.2
2002	14.5
2003	14.2
2004	14
2005	13.7
2006	13.2
2007	12.5
2008	11.8
2009	11
2010	9.9
2011	8.6
2012	7.4
2013	6.6