Year	Number of
1990	22.6
1991	22.74
1992	22.1
1993	20.83
1994	19.49
1995	18.41
1996	19.6
1997	21.52
1998	24.4
1999	27.8
2000	31.58
2001	33.64
2002	35.81
2003	38.18
2004	41.13
2005	44.99
2006	49.02
2007	54.02
2008	60.11
2009	66.83
2010	74.08
2011	79.08
2012	84.53
2013	90.78
2014	97.57
2015	104.86
2016	112.32