Year	Number
1970	3745
1971	3830
1972	4374
1973	4659
1974	5012
1975	5604
1976	6406
1977	7268
1978	7948
1979	8750
1980	9139
1981	10137
1982	11095
1983	11920
1984	12481
1985	12922
1986	13168
1987	13540
1988	13655
1989	13674
1990	14011
1991	14889
1992	15820
1993	16750
1994	17000
1995	17250
1996	17500
1997	17700