Year	Number of
1990	8.02
1991	8.46
1992	8.78
1993	9.01
1994	9.17
1995	9.28
1996	9.44
1997	9.71
1998	10.05
1999	10.4
2000	10.77
2001	11
2002	11.33
2003	12.07
2004	13.69
2005	16.58
2006	17.7
2007	19.93
2008	22.72
2009	25.55
2010	28.15
2011	31.35
2012	33.91
2013	35.85
2014	37.24
2015	38.21
2016	41.42