Year	Number of
1990	10
1991	10.44
1992	10.9
1993	11.2
1994	11.54
1995	11.93
1996	12.25
1997	12.63
1998	13.02
1999	13.41
2000	13.97
2001	14.36
2002	14.77
2003	15.23
2004	15.69
2005	16.4
2006	17.07
2007	17.58
2008	18.16
2009	18.8
2010	19.52
2011	20.22
2012	20.95
2013	21.74
2014	22.29
2015	22.91
2016	23.5