Year	Number of
1990	15.93
1991	16.3
1992	16.64
1993	16.97
1994	17.29
1995	17.68
1996	18.09
1997	18.56
1998	19.09
1999	19.41
2000	19.74
2001	19.95
2002	20.19
2003	20.46
2004	20.8
2005	20.72
2006	20.9
2007	21.1
2008	21.34
2009	21.8
2010	22.58
2011	23.39
2012	24.41
2013	26.06
2014	27.21
2015	29.08
2016	30.95