Year	Number
1971	34.73615
1972	35.15313
1973	35.01705
1974	34.7696
1975	35.92874
1976	35.95901
1977	36.06594
1978	36.76601
1979	35.9169
1980	35.10983
1981	25.54637
1982	27.63394
1983	27.45135
1984	26.90858
1985	25.95491
1986	25.4206
1987	23.70248
1988	23.14581
1989	22.99715
1990	23.10556
1991	24.34655
1992	24.27476
1993	23.56148
1994	23.22223
1995	23.53288
1996	21.79878
1997	22.46549