Year	Number of
1990	2.06
1991	2.03
1992	2.02
1993	2.01
1994	2.01
1995	2.01
1996	1.94
1997	1.88
1998	1.83
1999	1.78
2000	1.73
2001	1.66
2002	1.59
2003	1.53
2004	1.48
2005	1.42
2006	1.41
2007	1.4
2008	1.39
2009	1.38
2010	1.37
2011	1.41
2012	1.46
2013	1.51
2014	1.56
2015	1.62
2016	1.75