Year	Number
1971	19.85039
1972	19.64875
1973	20.83094
1974	19.28296
1975	17.7069
1976	19.07205
1977	17.06178
1978	17.40367
1979	16.53265
1980	16.64804
1981	15.57581
1983	16.05168
1984	17.40651
1985	17.41028
1986	22.9036
1987	24.28267
1989	23.45528
1991	26.98413
1992	28.03861
1993	24.60057
1994	24.08526
1995	26.02391
1996	20.7479