Year	Number
1970	46.75438
1971	45.88847
1972	45.52513
1973	46.59736
1974	49.05415
1975	53.55292
1976	49.77317
1977	50.16914
1978	46.17832
1979	41.53122
1981	43.32876
1982	39.75104
1983	39.65096
1984	38.23891
1985	34.23583
1986	33.27616
1987	33.0851
1988	32.97371
1989	33.11856
1990	34.889
1991	35.77675
1992	35.57033
1993	36.70085
1994	36.54312
1995	36.83172
1996	36.21515
1997	36.91207
1998	38.01943
1999	40.28437
2001	45.99111
2002	52.99786
2003	56.89936
2004	58.27379
2005	55.85542
2006	52.40834
2007	53.08766
2008	52.3892
2009	53.70457
2010	50.76274
2012	45.83178
2013	43.44315
2014	43.06031
2016	41.76673
2017	47.15284
2018	50.63304