Year	Number
1971	24.62705
1972	22.97945
1973	19.78955
1974	18.76202
1975	19.40129
1976	18.53399
1977	18.40195
1978	17.208
1979	17.30904
1980	14.80169
1981	11.4889
1982	11.02511
1983	11.84633
1984	12.30753
1985	14.31248
1986	15.31411
1987	16.01684
1988	14.82547
1989	14.42639
1990	14.45387
1991	19.94897
1992	18.33826
1993	20.40834
1994	17.28325
1995	20.22087
1996	21.27205
1997	22.6163
1998	21.79817
1999	22.50415
2000	22.43503
2001	19.97181
2002	25.08927
2003	23.63479
2004	23.32514
2005	23.80571
2006	22.62422
2007	20.78964
2013	36.87889
2014	44.50621
2016	39.68054
2017	38.7509