Year	Number of
1990	13.13
1991	14.19
1992	15.01
1993	15.77
1994	16.68
1995	17.8
1996	17.45
1997	17.42
1998	17.49
1999	17.8
2000	18.36
2001	17.66
2002	19.04
2003	20.39
2004	22.81
2005	26.71
2006	28.35
2007	31.63
2008	37.35
2009	42.61
2010	49.34
2011	52.85
2012	56.01
2013	58.85
2014	61.24
2015	62.87
2016	68.11