Year	Years
1800	471
1950	240.8
1960	134.8
1970	101.8
1983	43.3
1984	39
1985	37.4
1986	35.9
1987	34.5
1988	33.2
1989	32.1
1990	31
1991	30
1992	28.9
1993	27.9
1994	26.9
1995	25.9
1996	25
1997	24.1
1998	23.3
1999	22.5
2000	21.8
2001	21.1
2002	20.5
2003	20
2004	19.7
2005	19.4
2006	19.2
2007	19
2008	18.8
2009	18.7
2010	18.6
2011	18.5
2012	18.4
2013	18.1