Year	Number
1971	18.45833
1972	15.1828
1973	10.13103
1974	9.42949
1975	8.7043
1976	8.71481
1978	14.13004
1979	13.93392
1980	12.50172
1981	15.99327
1982	12.6305
1983	10.84409
1984	13.52716
1987	17.28611
1988	18.90133
1991	22.64899
1992	25.81818
1993	21.14929
1994	23.77551
1995	26.85817
1996	26.27314
1998	36.81748
2006	61.70549
2007	69.15319
2011	27.06564
2012	26.83722
2013	19.01047
2014	16.15861
2015	18.02736
2016	19.47935
2017	19.51205
2018	21.33152