Year	Number of
1990	18.46
1991	19.04
1992	19.64
1993	20.28
1994	20.94
1995	21.66
1996	22.4
1997	23.16
1998	23.96
1999	24.79
2000	25.68
2001	26.59
2002	27.56
2003	28.57
2004	29.65
2005	30.82
2006	32.04
2007	33.32
2008	34.71
2009	36.22
2010	37.89
2011	39.57
2012	41.41
2013	43.36
2014	45.48
2015	47.81
2016	50.48