Year	Number of
1990	2.04
1991	2.12
1992	2.2
1993	2.28
1994	2.37
1995	2.44
1996	2.48
1997	2.5
1998	2.52
1999	2.57
2000	2.6
2001	2.67
2002	2.76
2003	2.82
2004	2.88
2005	3.02
2006	3.08
2007	3.11
2008	3.12
2009	3.18
2010	3.25
2011	3.23
2012	3.24
2013	3.26
2014	3.38
2015	3.44
2016	3.45