Year	Number
1971	61.93421
1972	50.2377
1973	55.54688
1974	52.7029
1975	46.58209
1976	50.54887
1977	42.64063
1978	42.52778
1979	40.77778
1980	38.82635
1981	33.5913
1982	33.96226
1983	28.55015
1984	26.9621
1985	26.81792
1986	26.75824
1987	32.16993
1988	29.69688
1989	29.17015
1990	27.12766
1991	28.58747
1994	26.6481
1995	25.56456
1996	23.21525
1997	22.36461
1998	20.69155
1999	19.86042
2000	16.90323
2001	16.2291
2002	16.70442
2003	18.45809
2004	20.22118
2006	23.7209
2007	25.46163
2008	29.20404
2009	25.20381
2010	26.05711
2011	30.5374
2012	32.68218
2013	29.24426
2014	30.00836
2015	30.6783
2017	29.19395
2018	28.43509