Year	Number of
1990	15.85
1991	16.86
1992	18.1
1993	19.43
1994	20.76
1995	21.94
1996	22.95
1997	23.59
1998	23.95
1999	24.55
2000	24.85
2001	25.87
2002	27.14
2003	28.65
2004	30.13
2005	31.32
2006	33.49
2007	35.47
2008	37.72
2009	41.76
2010	44.85
2011	48.29
2012	53.65
2013	60.28
2014	67.16
2015	73.98
2016	81.01