Year	Number of
1990	2.02
1991	2.05
1992	2.09
1993	2.13
1994	2.17
1995	2.21
1996	2.27
1997	2.33
1998	2.39
1999	2.47
2000	2.55
2001	2.61
2002	2.69
2003	2.78
2004	2.86
2005	2.95
2006	3.02
2007	3.08
2008	3.13
2009	3.19
2010	3.26
2011	3.34
2012	3.44
2013	3.54
2014	3.65
2015	3.76
2016	3.88