Year	Number
1971	28.46432
1972	28.27855
1973	25.63455
1974	23.7552
1975	22.87335
1976	22.85845
1977	19.97146
1978	21.95287
1979	20.37171
1980	20.05676
1981	18.11492
1983	16.90346