Year	Number of
1990	11.76
1991	11.84
1992	12.01
1993	12.18
1994	12.38
1995	12.62
1996	12.8
1997	13.02
1998	13.26
1999	13.54
2000	13.87
2001	13.87
2002	13.9
2003	13.96
2004	14.05
2005	14.16
2006	14.6
2007	15.05
2008	15.52
2009	16.03
2010	16.56
2011	16.86
2012	17.17
2013	17.5
2014	17.84
2015	18.21
2016	19.38