Year	Number
1960	12.11677438776113
1961	12.6594411626574
1962	18.03131105615753
1963	16.82109065590673
1964	22.41174081187829
1965	20.645242753070733
1966	15.296397351881897
1967	14.430829237418415
1968	14.363835475915874
1969	12.835877582026015
1970	13.039433663550296
1971	12.634546807316926
1972	12.784997897616634
1973	12.607658137741337
1974	9.776675683677071
1975	11.572573866877507
1976	7.721641649198541
1977	5.885461825185581
1978	5.444435539436188
1979	4.583214068412753
1980	5.347391070323314
1981	8.22200704739258
1982	8.793082190959836
1983	9.626587909778017
1984	9.483592504858601
1985	9.68155066106722
1986	9.897843836398055
1987	10.334114259392729
1988	13.72356257098677
1989	15.74890402774828
1990	24.01815563594029
1991	15.398390229638473
1992	13.337945469670677
1993	8.542469051136603
1994	6.218451919404153
1995	6.8615071813477
1996	7.054555154196
1997	6.953252735689489
1998	6.723308453724909
1999	6.507282463792427
2000	6.233833119412764
2001	5.714246778292311
2002	4.5030310677826275
2003	3.701090144387447
2004	3.4821993990855105
2005	3.901663844737509
2006	3.594327703096114
2007	3.17979715541059
2008	3.6034915235190095
2009	3.7273072224433066
2010	4.331791159231206
2011	4.811031763862172
2012	4.6790111483634735
2013	4.869714270577373
2014	4.886370405959176
2015	4.64466724719305
2016	4.729834325997102
2017	4.76453801665368
2018	5.017477061333731
2019	4.709913250052172
2020	3.973419435516164
2021	4.072757428283058