Year	Number
1970	32.2938
1971	31.492
1972	31.18542
1973	31.12712
1974	27.74136
1975	29.37063
1976	28.84699
1978	28.14442
1979	27.96191
1980	27.38906
1981	26.84236
1982	26.02376
1983	25.53601
1984	25.30919
1985	25.07358
1986	24.76554
1987	25.06017
1988	25.36253
1989	24.96018
1990	24.6966
1991	24.7149
1992	22.89307
1993	24.16687
1994	24.14948
1995	22.30626
1996	21.47477
1997	20.675
2002	26.9585
2003	27.84307
2004	27.84345
2012	24.15974