Year	Number
1971	20.19048
1972	21.71429
1973	13.41379
1974	6.43382
1975	5.44737
1980	9.80508
1981	10.05714
1982	11.13077
1983	12.2625
1984	10.59735
1985	14.4902
1986	10.07865
1988	8.58387
1990	6.7765
1993	6.22029
1994	6.19138
1995	7.72266
1996	8.29137
1997	9.30022
1999	11.28598
2000	12.28212
2001	12.20481
2002	15.80907
2003	15.6728
2004	17.43802
2005	20.73634
2006	22.39084
2007	24.75347
2008	29.4073
2010	22.45965
2011	19.14205
2013	12.37628
2014	13.39215
2015	10.59756
2016	10.73031
2017	11.96552
2018	11.29744