Year	Measure
1800	682.7
1820	682.7
1920	1517
1921	1648
1922	1540
1923	1676
1924	1793
1925	1741
1926	1740
1927	1835
1928	1857
1929	2051
1930	2117
1931	1932
1932	1645
1933	1619
1934	1803
1935	2041
1936	2749
1937	2631
1938	2652
1939	2929
1940	3270
1941	3368
1942	3338
1943	2187
1944	2076
1945	2065
1946	2387
1947	2355
1948	2370
1949	2517
1950	2486
1951	2449
1952	2428
1953	2445
1954	2419
1955	2408
1956	2551
1957	2617
1958	2660
1959	2710
1960	2697
1961	2733
1962	2750
1963	2928
1964	2979
1965	3055
1966	3169
1967	3243
1968	3466
1969	3566
1970	3700
1971	3831
1972	4031
1973	4219
1974	4398
1975	4392
1976	4621
1977	4880
1978	5019
1979	5150
1980	5236
1981	5147
1982	4820
1983	4588
1984	4488
1985	4337
1986	4221
1987	4246
1988	4285
1989	4325
1990	4329
1991	4359
1992	4439
1993	4483
1994	4532
1995	4622
1996	4627
1997	4684
1998	4790
1999	4840
2000	4885
2001	4872
2002	4858
2003	4841
2004	4858
2005	4897
2006	5034
2007	5221
2008	5262
2009	5161
2010	5182
2011	5265
2012	5291
2013	5332
2014	5379
2015	5431
2016	5484
2017	5538
2018	5592