Year	Number
1970	29.23047
1971	29.22684
1972	30.08736
1973	29.49315
1974	29.44802
1975	31.216
1976	32.0461
1977	31.72408
1979	32.58065
1980	32.47697
1981	32.43437
1982	36.68085
1983	30.61007
1984	27.41088
1985	27.9232
1986	32.69003
1987	24.87229
1988	24.22307
1989	29.5071
1990	23.44796
1991	23.98157
1992	25.18852
1993	23.54378
1994	22.6386
1995	22.5894
1996	20.97789
1997	21.23775
1998	20.21772
1999	20.57751
2000	18.65127
2001	18.50602
2002	17.53494
2004	16.36115
2005	16.16496
2006	15.27497
2008	14.54534
2009	13.78091
2010	14.4155
2011	14.17028
2013	12.81121
2014	13.10042
2015	12.83307
2016	11.9319
2017	11.74043
2018	12.90757