Year	Number
1970	36.4844
1971	32.62978
1972	33.10174
1973	35.40067
1974	34.03709
1975	33.14135
1976	32.02958
1977	30.54283
1978	31.34217
1979	32.2155
1980	32.33898
1981	31.64659
1982	32.43714
1983	31.18365
1984	30.87607
1985	32.03553
1986	32.21477
1987	32.2979
1988	32.24975
1989	32.29417
1990	31.65654
1991	30.38869
1992	28.81411
1993	27.29929
1994	26.43662
1995	25.49106
1997	28.13585
1998	27.56744
1999	26.98536
2000	26.72295
2001	26.63306
2002	26.40132
2003	26.059
2004	25.84666
2005	25.55037
2006	25.39325
2007	25.22265
2008	25.08494
2009	25.51489
2012	23.41584
2013	22.61822
2014	22.41447
2015	23.71279