Year	Number of
1990	10.61
1991	11.12
1992	11.53
1993	11.88
1994	12.22
1995	12.59
1996	12.8
1997	12.79
1998	12.77
1999	12.72
2000	12.87
2001	13.46
2002	13.98
2003	14.77
2004	15.7
2005	16.87
2006	18.04
2007	19.24
2008	20.29
2009	21.38
2010	22.43
2011	24.27
2012	26.24
2013	27.9
2014	29.7
2015	31.61
2016	33.33