Year	Number
1970	32.63955
1971	26.22089
1972	23.09118
1973	24.13745
1974	23.24022
1975	24.19652
1976	23.68036
1977	23.66551
1978	24.7692
1979	25.70163
1980	27.09401
1981	27.09504
1982	32.91914
1983	26.73386
1984	26.40577
1985	21.8413
1986	21.5709
1987	18.56307
1988	18.89011
1989	19.26227
1990	16.84084
1991	17.36776
1992	17.2828
1993	17.58489
1994	16.70014
1995	16.96289
1996	16.81188
1997	17.29381
1998	17.73889
2000	16.85466
2001	15.88407
2002	15.10001
2003	14.59992
2004	13.32778
2005	15.5735
2006	15.57347
2007	13.32195
2008	11.73669
2009	12.37469
2010	13.00236
2011	13.36892
2012	15.23202
2013	14.92948
2014	12.50989
2017	12.6824
2018	12.68243