Year	Number
1970	7.68121
1971	8.37979
1972	8.44923
1973	8.26688
1974	7.88806
1975	10.65333
1976	9.48
1977	10.30544
1978	10.26339
1979	10.40523
1980	4.95402
1981	7.34109
1982	7.472
1983	6.91781
1984	8.57051
1985	9.02564
1986	9.44872
1987	10.20423
1988	9.84354
1989	13.14063
1990	10.29098
1991	12.39286
1992	11.25625
1993	14.12727
1994	13.58793
1995	12.35106
1996	9.66512
1997	8.98166
1998	9.28052
1999	9.75317
2000	10.68528
2001	12.18719
2002	11.67042
2003	14.26794
2004	11.50146
2005	11.44364
2006	10.49647
2007	10.78132
2008	9.78512
2009	8.14477
2010	8.98094
2011	8.29076
2012	8.94648
2013	8.75444
2014	8.2818
2015	8.08566
2016	7.94433
2017	8.31414