Year	Number
1971	30.33333
1972	28.90849
1973	27.99215
1974	27.65737
1975	27.26131
1976	26.9405
1977	25.59686
1978	23.77845
1979	23.99867
1980	22.99045
1981	22.20748
1982	20.92374
1983	20.80054
1984	21.0054
1985	21.51726
1986	22.77356
1987	22.77666
1988	21.96193
1989	21.72401
1990	21.37772
1991	20.51548
1992	19.31041
1993	18.86012
1994	18.78096
1995	18.39116
1996	18.73117
1997	15.41195
1999	18.26784
2000	17.72506
2001	17.19454
2002	19.02568
2003	18.94185
2004	17.60724
2005	17.72706
2006	16.46264
2007	15.63024
2008	14.75299
2009	14.2405
2010	13.75307
2011	13.44153
2012	13.77462
2013	13.59542
2014	13.39274
2015	11.91513
2016	11.86448
2017	12.03922