Year	Number of
1990	13.82
1991	14.1
1992	14.26
1993	14.37
1994	14.13
1995	13.72
1996	13.52
1997	13.5
1998	13.79
1999	14.04
2000	14.3
2001	14.54
2002	14.89
2003	15.1
2004	15.2
2005	15.32
2006	15.47
2007	15.74
2008	16.04
2009	16.35
2010	16.8
2011	17.19
2012	17.62
2013	18.14
2014	18.72
2015	19.14
2016	19.59