Year	Measure
1800	441.3
1820	443.4
1913	760.7
1950	5834
1951	6209
1952	6460
1953	6968
1954	7616
1955	7642
1956	8042
1957	8158
1958	8381
1959	9044
1960	9727
1961	10640
1962	11630
1963	12330
1964	13090
1965	14300
1966	15960
1967	16900
1968	17910
1969	18750
1970	19940
1971	22170
1972	24840
1973	28870
1974	32250
1975	30830
1976	31660
1977	34170
1978	33790
1979	33590
1980	34570
1981	35100
1982	33690
1983	28410
1984	26820
1985	23660
1986	21160
1987	21200
1988	21000
1989	20930
1990	23520
1991	25110
1992	24840
1993	23170
1994	22010
1995	21160
1996	20770
1997	20590
1998	20350
1999	19640
2000	20000
2001	19530
2002	19010
2003	19950
2004	20480
2005	21220
2006	21670
2007	22210
2008	23290
2009	22940
2010	23840
2011	25130
2012	26260
2013	26820
2014	27360
2015	28020
2016	28670
2017	29340
2018	30000