Year	Number
1970	4.414266010544815
1971	5.818692859736382
1972	7.120722285790936
1973	8.931853030648847
1974	16.206088078112295
1975	15.442315878432531
1976	11.684849887111584
1977	8.324007462577715
1978	6.383531934156164
1979	10.178399213255132
1980	9.394395807458869
1981	7.590082009026713
1982	5.974770302811143
1983	11.349921289956104
1984	10.629810451921264
1985	12.269252062115639
1986	9.793371316205247
1987	9.739491382426259
1988	5.091533105599774
1989	7.895215921447539
1990	11.859924778635598
1991	10.733031046868328
1992	7.834563321990222
1993	8.494641565330776
1994	8.962479773851024
1995	6.207236362393569
1996	10.630875708782392
1997	8.93491150017267
1998	6.840018982959845
1999	8.091833458899394
2000	7.412915800220119
2001	5.161241545562251
2002	6.753352999683079
2003	13.833493175782936
2004	10.311537780791951
2005	10.01807576045086
2006	9.026830385242697
2007	5.957596823175076
2008	7.026411739756266
2009	6.655603780566458
2010	5.562624021449559
2011	4.162361923465166
2012	3.600304109632698
2013	2.784865930835204
2014	3.503125813115242
2015	3.3715242661608156
2016	3.653817483190017