Year	Number of
1990	0.96
1991	0.98
1992	1
1993	1.02
1994	1.05
1995	1.07
1996	1.14
1997	1.23
1998	1.33
1999	1.44
2000	1.58
2001	1.61
2002	1.65
2003	1.7
2004	1.75
2005	1.8
2006	1.83
2007	1.86
2008	1.87
2009	1.89
2010	1.92
2011	1.95
2012	2
2013	2.05
2014	2.11
2015	2.16
2016	2.22