Year	Number
1961	2.1141649048625792
1962	2.456140350877193
1963	2.8526315789473684
1964	3.1862068965517243
1965	2.9310344827586206
1966	3.4482758620689653
1967	3.611302549965541
1968	4.063157894736842
1969	4.483636363636364
1970	4.578536947642035
1971	6.8500000000000005
1972	6.8500000000000005
1973	6.8500000000000005
1974	6.664864864864866
1975	6.664864864864866
1976	6.489473684210527
1977	6.489473684210527
1978	6.323076923076923
1979	6.323076923076923
1980	6.165
1981	6.165
1982	6.073891625615763
1983	6.044117647058823
1984	6.044117647058823
1985	5.360869565217391
1986	4.615384615384616
1987	4
1988	3.4782608695652173
1989	3.2564450474898234
1990	3.247631935047361
1991	3.216216216216216
1992	3.216216216216216
1993	3.2023681377825617
1994	3.216216216216216
1995	3.216216216216216
1996	3.216216216216216
1997	3.316216216216216
1998	4.162162162162162
1999	5.013513513513514
2000	5.854054054054054
2001	7.032432432432432
2002	8.9
2003	8.945945945945946
2004	10.424324324324324
2005	11.259459459459459
2006	11.478378378378379
2007	12.094594594594595
2008	12.462162162162162