Year	Number
1971	23.14286
1972	21.55455
1973	21.58841
1976	23.25166
1977	21.86452
1982	17.07342
1984	20.88728
1985	21.30919
1986	16.96916
1987	16.87257
1988	15.98807
1989	17.71429
1990	18.5987
1991	17.26316
1992	15.0458