Year	Number
1961	4.143820072289219
1962	4.227229594372731
1963	4.18443261124532
1964	4.191709871881496
1965	4.174887768052747
1966	4.829091179281347
1967	5.254022380738779
1968	5.534149126966694
1969	5.986559564015032
1970	6.7918539019865225
1971	7.338734089314645
1972	8.919348720492545
1973	8.223154902381463
1974	9.381956443626233
1975	9.916762134021665
1976	11.970356565671272
1977	15.153965981149591
1978	17.758963823708793
1979	20.25541822165919
1980	21.06581902682034
1981	24.979642875503952
1982	25.505838112843847
1983	29.545754794683646
1984	30.32339385103685
1985	29.29965194007927
1986	31.112096406506854
1987	33.64930592148134
1988	37.259684341667096
1989	40.01604506632686
1990	43.6808145778802
1991	43.51807273647385
1992	48.78798812827414
1993	46.69197849099091
1994	43.78766889438055
1995	49.88881379716374
1996	52.32069040138187
1997	53.4562870064389