Year	Number of
1990	14.16
1991	15.28
1992	16.29
1993	17.21
1994	17.74
1995	17.82
1996	18.11
1997	18.58
1998	19.05
1999	19.41
2000	19.68
2001	20.1
2002	20.67
2003	21.93
2004	23.77
2005	25.16
2006	26.32
2007	27.59
2008	28.69
2009	29.66
2010	30.4
2011	31.24
2012	32.08
2013	32.92
2014	33.76
2015	34.59
2016	35.19