Year	Number of
1990	2.2
1991	2.28
1992	2.35
1993	2.29
1994	2.3
1995	2.18
1996	2.11
1997	2.06
1998	2.08
1999	2.14
2000	2.23
2001	2.16
2002	2.15
2003	2.05
2004	2.02
2005	1.93
2006	1.87
2007	1.76
2008	1.74
2009	1.74
2010	1.7
2011	1.66
2012	1.63
2013	1.6
2014	1.63
2015	1.61
2016	1.72