Year	Number
1961	8.797054009819966
1962	9.387755102040817
1963	9.979633401221996
1964	10.569105691056912
1965	11.133603238866396
1966	11.915925626515763
1967	13.200000000000001
1968	13.846153846153847
1969	14.444444444444443
1970	15.055655296229803