Year	Number
1961	4636
1962	5748
1963	6620
1964	7011
1965	7293
1966	8500
1967	9700
1968	11000
1969	12200
1970	13500
1971	14776
1972	15000
1973	15200
1974	15400
1975	15576
1976	15826
1977	16256
1978	18755
1979	17560
1980	16350
1981	15170
1982	13976