Year	Number of
1990	15.7
1991	16.46
1992	17.27
1993	18.11
1994	19.03
1995	20.01
1996	20.97
1997	22.05
1998	23.21
1999	24.47
2000	25.64
2001	26.32
2002	27.28
2003	28.25
2004	29.31
2005	30.51
2006	31.62
2007	32.74
2008	33.98
2009	35.39
2010	36.83
2011	38.1
2012	39.52
2013	41.11
2014	42.86
2015	44.49
2016	46.15