Year	Measure
1800	515.5
1820	532.9
1950	1526
1960	2301
1961	2326
1962	2251
1963	2255
1964	2302
1965	2452
1966	2704
1967	2879
1968	3159
1969	3350
1970	3765
1971	3886
1972	4129
1973	4531
1974	4953
1975	5854
1976	6726
1977	7349
1978	7940
1979	8587
1980	9104
1981	9402
1982	9683
1983	9752
1984	10020
1985	10480
1986	10770
1987	11110
1988	11940
1989	12810
1990	13490
1991	14220
1992	14750
1993	15260
1994	15980
1995	16780
1996	17360
1997	18050
1998	18580
1999	19170
2000	20280
2001	19800
2002	20160
2003	19970
2004	19870
2005	20410
2006	20820
2007	21510
2008	22210
2009	21460
2010	22030
2011	22310
2012	22460
2013	22720
2014	23110
2015	23530
2016	23990
2017	24410
2018	24820