Year	Number of
1990	2.35
1991	2.49
1992	2.6
1993	2.68
1994	2.72
1995	2.89
1996	3.04
1997	2.86
1998	2.79
1999	2.94
2000	3.01
2001	3.13
2002	3.2
2003	3.16
2004	3.13
2005	3.06
2006	3.01
2007	2.93
2008	2.83
2009	2.95
2010	3.14
2011	3.23
2012	3.32
2013	3.4
2014	3.49
2015	3.57
2016	3.63