Year	Number
1971	34.82114
1972	34.01514
1973	33.59355
1974	32.91377
1975	31.49028
1976	30.35173
1977	29.42885
1978	28.90115
1979	28.9276
1980	27.76282
1981	27.33912
1982	26.69948
1983	26.02124
1984	26.39321
1985	26.03711
1986	25.62331
1987	25.68126