Year	Number of
1990	11.21
1991	11.61
1992	12.06
1993	12.54
1994	13.12
1995	13.75
1996	13.84
1997	13.89
1998	14.05
1999	14.34
2000	14.69
2001	15.02
2002	15.37
2003	15.71
2004	16.07
2005	16.45
2006	17.14
2007	17.86
2008	18.63
2009	19.45
2010	20.33
2011	20.99
2012	21.68
2013	22.4
2014	23.15
2015	23.91
2016	25.9