Year	Number of
1990	4.06
1991	4.29
1992	4.52
1993	4.75
1994	5.02
1995	5.32
1996	5.55
1997	5.75
1998	6.06
1999	6.22
2000	6.7
2001	7.14
2002	7.57
2003	8
2004	8.45
2005	9.02
2006	9.56
2007	10.05
2008	10.44
2009	10.8
2010	11.26
2011	11.68
2012	12.17
2013	12.66
2014	13.16
2015	13.66
2016	14.28