Year	Number of
1990	21.53
1991	22.64
1992	23.72
1993	24.77
1994	25.84
1995	26.96
1996	28.28
1997	29.63
1998	31.07
1999	32.6
2000	34.24
2001	35.95
2002	37.76
2003	39.72
2004	41.81
2005	44.05
2006	46.09
2007	48.27
2008	50.68
2009	53.2
2010	55.88
2011	58.43
2012	61.11
2013	63.93
2014	66.98
2015	70.32
2016	73.87