Year	Number
1961	14.275660003455062
1962	14.738128261013143
1963	14.608672771059808
1964	14.8676034213903
1965	15.11117654516381
1966	16.322578849553555
1967	16.62705318694092
1968	16.70710749697228
1969	16.7956244964278
1970	18.060534442673724
1971	18.49171468161681
1972	20.293303324223427
1973	21.899967271817186
1974	23.26140853019431
1975	23.558148493572848
1976	24.110832148582837
1977	25.740475630862587
1978	26.96640071918193
1979	27.46845658944688
1980	26.81029708234564
1981	28.270512022500405
1982	27.71766896379469
1983	27.518455807653233