Year	Number of
1990	15.21
1991	15.88
1992	16.63
1993	17.47
1994	18.4
1995	19.34
1996	20.34
1997	21.02
1998	21.67
1999	22.49
2000	23.13
2001	24.17
2002	25.3
2003	26.21
2004	27.61
2005	30
2006	31.46
2007	37.38
2008	41.17
2009	45.25
2010	49.32
2011	54.36
2012	59.16
2013	63.73
2014	68.4
2015	73.45
2016	78.17