Year	Number of
1990	15.28
1991	16.16
1992	16.79
1993	17.81
1994	18.57
1995	19.27
1996	19.56
1997	20.22
1998	21.15
1999	22.54
2000	23.46
2001	23.2
2002	25.11
2003	26.97
2004	28.25
2005	28.66
2006	29.81
2007	31.87
2008	34.9
2009	38.54
2010	41.81
2011	44.5
2012	47.97
2013	50.03
2014	54.62
2015	59.04
2016	64.08