Year	Number
1961	7485
1962	8505
1963	9300
1964	10190
1965	10470
1966	11430
1967	12395
1968	13765
1969	15505
1970	16360
1971	16005
1972	16655
1973	17830
1974	19535
1975	19250
1976	21100
1977	22850
1978	24300
1979	25600
1980	26800
1981	26500
1982	26800
1983	27475
1984	26870
1985	26254
1986	28248
1987	28662
1988	28444
1989	28400
1990	27400
1991	25920
1992	25790
1993	25500
1994	25300
1995	24900
1996	24620
1997	24345
1998	24065
1999	23785
2000	23500
2001	23230
2002	22950
2003	22670
2004	22395
2005	22115
2006	21850
2007	21560
2008	21280