Year	Number
1971	17927
1972	18437
1973	18673
1974	18477
1975	17811
1976	20215
1977	20145
1979	17744
1980	18037
1981	18093
1982	17945
1983	17807
1984	17353
1985	17130
1986	16783
1987	16733
1988	16660
1989	15516