Year	Number of
1990	8.51
1991	8.75
1992	9.02
1993	9.29
1994	9.61
1995	9.96
1996	10.23
1997	10.55
1998	10.74
1999	10.91
2000	11.12
2001	11.24
2002	11.27
2003	11.44
2004	11.43
2005	11.63
2006	11.9
2007	12.04
2008	12.58
2009	12.87
2010	13.38
2011	13.92
2012	14.41
2013	14.86
2014	15.33
2015	15.83
2016	16.39