Year	Number of
1990	11.23
1991	11.39
1992	11.54
1993	11.45
1994	11.47
1995	11.6
1996	11.75
1997	11.94
1998	11.85
1999	11.65
2000	11.67
2001	11.98
2002	12.05
2003	12.12
2004	12.54
2005	12.95
2006	13.47
2007	13.97
2008	14.32
2009	14.66
2010	14.91
2011	15.28
2012	15.76
2013	16.23
2014	16.93
2015	17.49
2016	18.4