Year	Number
1970	41.17791
1971	40.8534
1972	41.24468
1973	42.45591
1974	42.65017
1975	42.09882
1976	42.20764
1977	42.23202
1978	41.9182
1979	42.12435
1980	42.64596
1981	42.67621
1982	42.43642
1983	42.05844
1984	41.6558
1985	41.61673
1986	41.62096
1987	41.62835
1988	42.23038
1989	42.26232
1990	42.3503
1991	42.13674
1992	41.9359
1993	41.69417
1994	41.50884
1995	41.25163
1996	40.9494
1997	40.61478
1998	40.29641
1999	40.04525
2000	39.87987
2001	40.1594
2002	40.73892
2003	41.0148
2004	40.99374
2005	40.78047
2006	40.62981
2007	40.32514
2008	39.30997
2009	38.23183
2010	37.15236
2011	35.84928
2012	35.8043
2013	33.48807
2014	32.788
2015	32.7214
2016	35.55419
2017	33.24849
2018	33.24669