Year	Number of
1990	20.92
1991	21.8
1992	22.93
1993	24.13
1994	25.43
1995	26.78
1996	27.68
1997	28.46
1998	29.19
1999	29.89
2000	30.66
2001	32.09
2002	33.7
2003	35.64
2004	37.88
2005	40.46
2006	42.45
2007	44.73
2008	47.44
2009	50.32
2010	53.33
2011	55.62
2012	57.97
2013	60.39
2014	62.85
2015	65.36
2016	67.85