Year	Number of
1990	2.04
1991	1.96
1992	1.88
1993	1.81
1994	1.72
1995	1.65
1996	1.66
1997	1.67
1998	1.68
1999	1.7
2000	1.72
2001	1.73
2002	1.76
2003	1.76
2004	1.77
2005	1.74
2006	1.71
2007	1.65
2008	1.6
2009	1.6
2010	1.63
2011	1.65
2012	1.69
2013	1.74
2014	1.78
2015	1.79
2016	1.79