Year	Number
1971	4.84106
1975	7.47706
1977	10.24642
1978	9.36889
1979	9.81352
1980	10.79959
1982	9.46947
1983	11.60721
1987	7.74266
1997	17.18467
1998	17.39573
1999	19.43958
2000	20.50987
2016	25.22213
2017	30.81621