Year	Number
1971	16.8477
1973	23.54059
1981	43.807
1982	48.26364
1983	45.81546
1984	42.41492
1985	38.10382
1986	37.50088
1987	35.21323
1988	34.29832
1989	35.57241
1990	34.9536
1991	32.57161
1994	43.11157
1995	45.02911
1997	44.41581
1998	46.48057
1999	47.76229
2000	50.12283
2001	52.94991
2002	56.28967
2003	56.23746
2004	55.05284
2005	53.21143
2006	50.42275
2007	50.8791
2008	48.53713
2009	49.07538
2010	48.44957
2011	47.29163
2012	45.72134
2013	46.92711
2014	44.63494
2015	45.52116
2016	42.53404
2017	41.66267
2018	41.7035