Year	Number
1971	14.59574
1972	23.87805
1973	19.14815
1974	14.23288
1975	30.9
1976	37.73684
1977	23.84091
1978	26.51515
1979	27
1982	21.71711
1983	24.25954
1984	23.11039
1985	22.32903
1986	19.67206
1987	29.07595
1988	18.81818
1989	17.74074
1990	17.05307
1991	18.223
1992	15.92157
1993	16.96839
1994	22.97959
1995	22.4702
1996	21.86293
1999	20.62435
2000	20.63084
2001	17.23748
2002	16.52351
2003	16.05241
2004	15.16387
2005	16.546
2006	17.88662
2007	17.00684
2008	16.57175
2009	15.28236
2011	14.65541
2013	15.4222
2014	13.92013
2015	14.16722
2016	14.54416
2017	14.3971
2018	14.8318