Year	Number of
1990	8.51
1991	9.2
1992	9.86
1993	10.53
1994	11.28
1995	12.15
1996	11.79
1997	11.54
1998	11.39
1999	11.29
2000	11.23
2001	11.53
2002	11.91
2003	12.4
2004	13.06
2005	13.93
2006	14.86
2007	16.04
2008	17.46
2009	19.09
2010	20.86
2011	22.67
2012	24.59
2013	26.59
2014	28.6
2015	30.64
2016	33.47