Year	Number of
1990	5.23
1991	5.54
1992	5.68
1993	5.79
1994	5.96
1995	6.05
1996	6.64
1997	7.29
1998	8.04
1999	8.81
2000	9.49
2001	9.63
2002	9.84
2003	10.15
2004	10.91
2005	12.59
2006	12.87
2007	13.56
2008	14.37
2009	15.26
2010	15.83
2011	16.17
2012	16.59
2013	17.17
2014	17.67
2015	18.46
2016	20.17