Year	Number
1971	47.69017
1972	48.54799
1973	48.83465
1974	51.42933
1975	51.62818
1976	50.56058
1977	49.78232
1978	50.0225
1979	50.47961
1980	51.52335
1981	51.53402
1982	50.50649
1983	48.61283
1984	50.39807
1985	50.94533
1986	50.75656
1987	50.24782
1988	51.30844
1989	50.50546
1990	51.484
1991	51.10971
1992	47.86434
1995	46.29539
1997	48.78088
1998	51.78101
1999	51.86201
2001	62.72134
2002	60.80479
2003	57.0638
2004	53.90314
2005	47.8128
2006	44.69425
2007	44.43054
2008	46.03527
2009	46.31569
2010	45.79474
2011	45.43773
2012	45.56349
2014	44.19526
2015	41.46571
2016	42.73541
2017	44.61321
2018	44.83412