Year	Number
1971	32.98561
1972	34.86698
1973	31.6495
1974	34.31852
1975	32.99378
1976	30.67352
1977	32.082
1978	32.21813
1979	30.68591
1980	26.98421
1981	27.35145
1982	28.43166
1983	28.29644
1984	28.83651
1985	24.09774
1986	24.35387
1987	24.20308
1988	22.78133
1989	21.89308
1990	20.86278
1991	18.25488
1992	21.22331
1993	22.11671
1994	17.82751
1995	16.51201
1996	15.6904
1997	15.70862
1998	15.24417
1999	17.84348
2000	14.56081
2001	14.51021
2002	18.02273
2003	17.25032
2004	16.65013
2005	17.02743
2006	17.19521
2007	16.84106
2008	18.6382
2009	20.49455
2010	20.10442
2011	20.65793
2012	21.27306
2013	21.81077
2014	22.4379
2015	21.72681
2016	21.40312
2017	20.3839
2018	19.32357