Year	Number of
1990	14.79
1991	15.34
1992	15.87
1993	16.47
1994	17.13
1995	17.87
1996	18.54
1997	19.32
1998	19.94
1999	20.7
2000	21.83
2001	22.46
2002	23.37
2003	23.68
2004	24.3
2005	25.26
2006	26.16
2007	26.88
2008	27.47
2009	28.34
2010	29.03
2011	29.71
2012	30.41
2013	31.12
2014	31.94
2015	32.84
2016	33.77