Year	Number
1981	9.59374
1982	9.59374
1983	9.903
1984	10.08634
1985	9.58791
1986	9.21208
1987	8.81661
1988	8.79376
1989	10.75784
1990	10.66269
1991	10.37314
1992	10.03013
1993	9.73872
1994	8.52716
1995	9.53653
1996	12.2081
1997	12.52497
1999	14.67919
2000	17.50182
2001	18.93222
2002	20.99164
2003	22.19104
2004	22.3331
2005	20.8529
2006	21.19021
2007	18.85787
2008	17.38704
2009	16.21524
2010	16.25751
2011	16.38107
2012	15.08019
2013	14.22373
2014	13.00711
2015	12.56121
2016	12.34178
2017	11.80775