Year	Number of
1990	9.58
1991	9.69
1992	9.79
1993	9.91
1994	10.02
1995	10.13
1996	10.3
1997	10.51
1998	10.75
1999	11.02
2000	11.35
2001	11.45
2002	11.59
2003	11.74
2004	11.85
2005	11.92
2006	12.69
2007	13.44
2008	14.27
2009	15.28
2010	16.57
2011	17.36
2012	18.4
2013	19.55
2014	20.71
2015	21.81
2016	22.84