Year	Number
1961	2.3474903474903477
1962	2.3524904214559386
1963	2.3587786259541983
1964	2.5894897182025893
1965	2.9969650986342944
1966	3.2477341389728096
1967	6.842105263157896
1968	8.783783783783784
1969	10.768072289156628
1970	12.781954887218044
1971	14.628657164291074
1972	16.15497076023392
1973	17.99709724238026
1974	19.841040462427745
1975	20.02830856334041
1976	20.23643949930459
1977	19.960079840319363
1978	20.47872340425532
1979	21.4190093708166
1980	22.371967654986523
1981	23.22754895340986
1982	24.119241192411923
1983	25.0852079072938
1984	25.956284153005466
1985	26.92783505154639
1986	27.842866988283944
1987	28.834142956280363
1988	29.874213836477985
1989	30.394190871369293
1990	30.91655266757866
1991	31.16621983914209
1992	31.353135313531354
1993	28.960190136660724
1994	29.878787878787875
1995	31.156250000000004
1996	31.5
1997	33.55263157894737
1998	33.91447368421053
1999	35.42234332425068
2000	48.68913857677903