Year	Number of
1990	2.89
1991	2.94
1992	3.06
1993	3.12
1994	3.15
1995	3.22
1996	3.28
1997	3.35
1998	3.44
1999	3.52
2000	3.58
2001	3.64
2002	3.72
2003	3.82
2004	3.93
2005	4.01
2006	4.15
2007	4.27
2008	4.39
2009	4.48
2010	4.61
2011	4.74
2012	4.87
2013	5.01
2014	5.15
2015	5.26
2016	5.4