Year	Number
1961	14.275528583443426
1962	14.737837146135874
1963	14.608309509406233
1964	14.867168053589369
1965	15.110598677589197
1966	16.32198789839166
1967	16.626240876104557
1968	16.7061493982008
1969	16.794848733835487
1970	18.059198248160705
1971	18.489942935099073
1972	20.291162416826687
1973	21.897482793473554
1974	23.2586194733076
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
1984	26.50647450831663
1985	25.322231542755357
1986	24.026768529793
1987	23.205042741745746