Year	Number of
1990	13.52
1991	12.85
1992	12.21
1993	11.67
1994	11.33
1995	11.2
1996	11.48
1997	12.09
1998	12.94
1999	13.99
2000	15.09
2001	16.11
2002	17.05
2003	17.75
2004	18.54
2005	19.49
2006	20.56
2007	21.85
2008	23.31
2009	24.84
2010	26.43
2011	27.57
2012	28.7
2013	29.84
2014	31.04
2015	32.3
2016	33.62