Year	Number of
1990	11.84
1991	12.04
1992	12.21
1993	12.37
1994	12.56
1995	12.81
1996	13.05
1997	13.27
1998	13.49
1999	13.75
2000	13.95
2001	14.21
2002	14.63
2003	15.03
2004	15.47
2005	16.04
2006	16.41
2007	16.76
2008	17.16
2009	17.59
2010	18.1
2011	18.78
2012	19.47
2013	20.23
2014	21.15
2015	22.05
2016	22.97