Year	Measure
1800	698.1
1820	698.1
1913	1288
1970	10120
1971	10650
1972	11050
1973	11410
1974	11940
1975	12160
1976	12810
1977	17340
1978	18340
1979	19050
1980	20510
1981	20570
1982	20010
1983	19720
1984	19180
1985	18590
1986	17390
1987	17410
1988	17490
1989	18680
1990	18830
1991	19080
1992	19630
1993	20520
1994	21690
1995	22160
1996	22680
1997	23270
1998	22900
1999	22750
2000	22280
2001	22610
2002	22600
2003	22740
2004	22760
2005	22700
2006	22840
2007	23190
2008	23360
2009	22890
2010	22580
2011	22340