Year	Number
1964	4.930120481927711
1965	7.175609756097561
1966	3.1899749373433584
1967	2.570254110612855
1968	3.1385813148788926
1969	7.0421926910299
1970	3.3355844155844157
1971	5.07023656748572
1972	5.064011355203635
1973	3.1622651968229323
1974	4.390026393444391
1975	2.6084914744798664
1976	1.3355693596707037
1977	1.256910417973964
1978	1.3156101008869356
1979	0.9841076524804242
1980	0.9022857224731907
1981	1.0902837825619325
1982	1.4572726869504078
1983	1.6880049646757198
1984	1.8625361638642706
1985	2.0316888775952684
1986	1.8589815586559029
1987	2.2232267406877586
1988	3.453135476106391
1989	5.356564069400038
1990	8.51945782266399
1991	2.4286947834687616
1992	3.5765424130785433
1993	5.648353558786683
1994	3.2920009859822725
1995	2.426597908836667
1996	2.0907498313144415
1997	1.911259706668517
1998	1.7358288328280242
1999	1.6969762864679565
2000	1.53625362367268
2001	1.266858960396394
2002	1.1804689807225035
2003	1.3926111715015814
2004	1.0409141770694308
2005	1.5717903982160955
2006	1.3509441994411224
2007	0.885342291610748
2008	1.057063255056815
2009	0.8054586990420317
2010	1.1813829790112589
2011	1.66316092827695
2012	2.78171360093185
2013	2.1489286157739884
2014	1.6518357765491507
2015	1.9337557223876414
2016	1.740163310655906
2017	1.5466156982232762
2018	1.5429869380175985
2019	1.57571761564872
2020	1.5518591029679032