Year	Number of
1990	12.7
1991	13.27
1992	13.86
1993	14.51
1994	15.19
1995	15.94
1996	16.36
1997	16.84
1998	17.38
1999	17.89
2000	18.34
2001	19.13
2002	19.89
2003	20.65
2004	21.49
2005	22.44
2006	23.11
2007	23.86
2008	24.67
2009	25.51
2010	26.38
2011	26.98
2012	27.59
2013	28.22
2014	28.91
2015	29.68
2016	30.52