Year	Number of
1990	10.05
1991	10.36
1992	10.7
1993	11.07
1994	11.51
1995	11.95
1996	12.12
1997	12.07
1998	12.09
1999	12.29
2000	12.57
2001	12.65
2002	12.63
2003	12.58
2004	12.42
2005	12.45
2006	12.52
2007	12.48
2008	12.77
2009	13.23
2010	13.68
2011	14.46
2012	14.99
2013	15.42
2014	15.99
2015	16.86
2016	17.85