Year	Number
1971	12.42298
1972	12.67571
1973	12.66609
1974	13.31095
1975	13.16924
1976	14.0555
1977	13.61807
1978	14.53177
1979	13.75995
1980	13.54637
1981	12.17765
1983	11.10759