Year	Number of
1990	11.07
1991	11.93
1992	12.83
1993	13.79
1994	14.81
1995	15.91
1996	17
1997	18
1998	19.07
1999	20
2000	20.91
2001	22.38
2002	24.04
2003	25.68
2004	27.41
2005	29.25
2006	30.65
2007	32.05
2008	33.6
2009	35.3
2010	37.23
2011	38.86
2012	40.78
2013	42.92
2014	45.2
2015	47.58
2016	50.14