Year	Number
1971	4.56863
1972	4.53704
1973	4.46296
1974	4.50909
1975	3.73023
1976	4.49327
1979	6.91935
1980	7.72294
1985	5.63982
1986	5.95931
1987	5.91126
1988	6.84696
1989	6.616
1991	8.23853
1992	7.10575
1993	7.65468
1999	13.29024
2000	11.70229
2001	12.40434
2002	17.34539
2004	23.47683
2005	16.0942
2009	16.3349
2010	16.40639
2011	15.72018
2012	20.2122
2013	14.67375
2014	25.23399
2016	22.20748
2017	19.79602