Year	Number of
1990	3.38
1991	3.41
1992	3.44
1993	3.5
1994	3.5
1995	3.53
1996	3.54
1997	3.55
1998	3.58
1999	3.62
2000	3.67
2001	3.75
2002	3.88
2003	4.03
2004	4.17
2005	4.31
2006	4.47
2007	4.61
2008	4.72
2009	4.82
2010	4.95
2011	5.09
2012	5.25
2013	5.42
2014	5.59
2015	5.76
2016	5.95