Year	Number of
1990	3.01
1991	3.34
1992	3.69
1993	4.07
1994	4.51
1995	5.02
1996	5.26
1997	5.56
1998	5.84
1999	6.14
2000	6.44
2001	6.61
2002	6.78
2003	6.98
2004	7.19
2005	7.41
2006	7.95
2007	8.54
2008	9.25
2009	10.03
2010	10.87
2011	11.38
2012	11.94
2013	12.45
2014	13.03
2015	13.66
2016	14.37