Year	Number of
1990	18.45
1991	18.35
1992	18.32
1993	18.24
1994	19
1995	20.98
1996	21.36
1997	22.15
1998	22.81
1999	22.38
2000	22.47
2001	22.98
2002	24.24
2003	25.46
2004	25.09
2005	26.32
2006	25.87
2007	26.25
2008	26.78
2009	27.67
2010	28.17
2011	29.39
2012	29.97
2013	31.61
2014	32.9
2015	34.1
2016	35.84