Year	Number of
1990	9.63
1991	9.81
1992	9.94
1993	10.07
1994	10.15
1995	10.23
1996	10.33
1997	10.4
1998	10.23
1999	10.49
2000	10.48
2001	10.51
2002	10.72
2003	11.13
2004	11.71
2005	12.01
2006	12.36
2007	12.94
2008	13.33
2009	14.29
2010	15
2011	15.79
2012	17.05
2013	17.93
2014	18.89
2015	19.85
2016	20.82