Year	Number of
1990	13.3
1991	13.54
1992	14.05
1993	14.44
1994	14.65
1995	14.73
1996	15.17
1997	15.85
1998	16.86
1999	18.1
2000	19.57
2001	20.2
2002	20.81
2003	22.1
2004	23.35
2005	24.61
2006	25.35
2007	26.22
2008	27.19
2009	28.32
2010	29.71
2011	30.5
2012	31.58
2013	31.74
2014	31.71
2015	32.04
2016	32.65