Year	Number of
1990	16.36
1991	17.62
1992	18.58
1993	20.31
1994	21.87
1995	23.42
1996	24.81
1997	25.71
1998	26.19
1999	27.19
2000	28.15
2001	28.46
2002	29.8
2003	30.21
2004	30.32
2005	30.74
2006	31.48
2007	31.7
2008	32.84
2009	33.58
2010	33.67
2011	34.12
2012	34.14
2013	34.79
2014	34.92
2015	36.08
2016	37.56