Year	Number of
1990	5.07
1991	5.29
1992	5.54
1993	5.8
1994	6.11
1995	6.24
1996	6.95
1997	7.79
1998	8.75
1999	9.51
2000	10.45
2001	10.94
2002	11.47
2003	12.12
2004	12.95
2005	13.76
2006	14.81
2007	15.78
2008	16.75
2009	17.92
2010	19.23
2011	19.85
2012	20.53
2013	21.35
2014	22.19
2015	23.07
2016	23.91