Year	Measure
1800	584
1820	584
1913	381.1
1950	321.6
1951	325.3
1952	328.9
1953	342.1
1954	336.2
1955	348
1956	353.1
1957	344.2
1958	349
1959	351.8
1960	362.8
1961	373.3
1962	381
1963	422.9
1964	434.9
1965	451.2
1966	459.1
1967	468.8
1968	466.9
1969	473.9
1970	490.4
1971	500.3
1972	514.3
1973	519.5
1974	513.8
1975	502.7
1976	503.6
1977	505.8
1978	491.9
1979	517.1
1980	534.4
1981	531
1982	524.9
1983	536.5
1984	513.9
1985	472.4
1986	491.5
1987	521.1
1988	512.6
1989	501.9
1990	476.6
1991	526.1
1992	582.9
1993	658.7
1994	795
1995	806.5
1996	866.1
1997	913.5
1998	905.3
1999	877.6
2000	741.6
2001	775.2
2002	765.4
2003	713.6
2004	694.4
2005	685
2006	655.2
2007	642.9
2008	562
2009	566.1
2010	561.1
2011	591.2
2012	613.7
2013	615.7
2014	611
2015	604.9
2016	600.5
2017	590
2018	579.9