Year	Number
1970	26.55341
1974	28.2925
1976	25.82344
1980	22.58283
1982	20.70478
1983	23.74809
1984	24.69212
1987	20.22725
1988	21.36057
1991	19.01113
1993	16.19213
1995	20.23403
1997	18.40688
2004	18.47639
2007	18.46583