Year	Number of
1990	13.14
1991	13.83
1992	14.58
1993	15.39
1994	16.28
1995	17.23
1996	17.68
1997	18.15
1998	18.68
1999	19.26
2000	19.9
2001	20.3
2002	20.78
2003	21.25
2004	21.77
2005	22.32
2006	22.98
2007	23.66
2008	24.39
2009	25.19
2010	26.07
2011	26.91
2012	27.81
2013	28.83
2014	29.88
2015	30.95
2016	32.09