Year	Number
1971	59.65253
1972	56.52971
1973	52.65621
1974	51.14466
1975	49.23848
1976	50.05248
1977	53.19814
1978	56.99693
1979	60.61495
1980	55.91792
1981	51.65228
1982	49.60707
1983	47.4752
1984	46.7123
1985	47.35577
1986	48.45892
1987	48.94776
1988	49.73915
1989	50.20987
1990	50.10489
1991	50.5765
1992	54.2653
1997	57.07631
1998	56.64065
1999	54.30548
2000	54.02683
2001	51.41724
2002	58.96519
2003	59.90567
2004	62.02973
2005	68.95194
2006	65.93305
2007	69.28601
2008	67.73053
2009	68.29941
2010	64.61867
2011	58.09439
2012	59.27851
2013	59.81633
2014	58.24871
2015	58.34317
2016	58.45684
2017	57.85938
2018	59.50859