Year	Number of
1990	1.54
1991	1.57
1992	1.59
1993	1.59
1994	1.61
1995	1.63
1996	1.66
1997	1.67
1998	1.76
1999	1.71
2000	1.72
2001	1.67
2002	1.66
2003	1.72
2004	1.82
2005	1.87
2006	1.9
2007	1.93
2008	1.92
2009	2.01
2010	2.07
2011	2.16
2012	2.22
2013	2.27
2014	2.33
2015	2.4
2016	2.44