Year	Number
1971	44.4519
1972	47.15783
1973	47.18339
1974	45.03279
1975	47.49876
1976	47.10611
1977	47.78169
1978	49.92135
1979	52.32026
1980	52.9596
1981	54.48514
1982	59.78713
1983	60.34866
1984	57.70058
1985	56.49009
1986	57.7585
1987	67.54567
1988	64.77544
1989	57.35904
1990	55.1772
1991	56.65663
1992	57.83011
1993	59.77943
1994	58.25553
1995	50.97969
1996	49.93909
1998	46.50149
1999	49.00318
2000	48.8764
2001	47.4189
2002	45.37812
2003	44.65893
2004	48.69293
2005	47.17637
2006	45.83142
2007	47.65745
2008	48.92155
2009	48.90026
2010	52.39988
2011	52.68641
2012	48.23903
2013	46.09623
2014	44.49899
2015	42.17715
2016	41.54927
2017	40.68126
2018	39.72173