Year	Number
1970	16.33148
1976	11.74583
1977	13.86392
1978	9.78814
1979	18.88069
1980	19.3258
1981	19.10693
1982	19.83159
1983	26.32223
1984	28.71523
1985	28.48415
1986	26.74049
1987	21.65938
1988	17.79545
1990	19.3482
1999	20.48241
2000	19.75483
2001	22.49314
2002	20.55115
2003	19.1203
2004	16.68625
2005	17.43121
2006	17.80003
2007	18.80327
2008	21.02576
2009	26.94853
2011	25.95656
2012	23.08715
2014	22.87295
2016	28.96697
2017	30.34408
2018	37.11937