Year	Number
1970	29.81041
1971	29.52923
1972	29.07381
1973	28.89498
1974	29.09919
1975	29.06935
1976	28.20913
1979	26.72512
1980	27.68133
1981	33.02539
1982	31.63091
1983	31.9309
1984	33.78534
1985	31.48334
1986	32.27696
1987	31.48959
1988	31.9293
1989	32.28807
1990	31.88081
1991	32.19896
1992	32.29903
1993	32.44083
1994	31.37283
1995	30.60893
1996	29.54329
1997	28.61276
1998	27.52934
1999	26.82207
2000	24.94075
2001	24.31442
2002	22.59585
2004	22.34571
2005	21.34285
2006	19.70728
2007	19.494
2008	18.97453
2009	18.40435
2010	17.8517
2011	17.34208
2013	13.34199
2014	13.22687
2015	12.6763
2016	11.97865
2017	11.62825
2018	12.2047