Year	Number of
1990	7.57
1991	8.08
1992	8.62
1993	9.17
1994	9.7
1995	10.17
1996	10.4
1997	10.51
1998	10.54
1999	10.59
2000	10.72
2001	10.97
2002	11.41
2003	11.97
2004	12.54
2005	13.07
2006	14.25
2007	15.41
2008	16.65
2009	17.93
2010	19.31
2011	19.85
2012	20.32
2013	20.72
2014	21.18
2015	21.73
2016	22.16