Year	Number of
1990	9.5
1991	9.83
1992	10.16
1993	10.44
1994	10.73
1995	11.08
1996	11.36
1997	11.63
1998	11.93
1999	12.32
2000	12.72
2001	13.38
2002	14.07
2003	14.88
2004	15.9
2005	16.86
2006	17.8
2007	18.89
2008	19.99
2009	21.13
2010	22.36
2011	23.78
2012	25.44
2013	27.09
2014	28.66
2015	30.29
2016	31.96