Year	Number of
1990	15.36
1991	15.76
1992	16.16
1993	16.6
1994	17.05
1995	17.51
1996	18.06
1997	18.67
1998	19.35
1999	20.11
2000	20.97
2001	21.94
2002	23.02
2003	24.18
2004	25.31
2005	26.36
2006	28.3
2007	30.23
2008	32.37
2009	34.99
2010	38.35
2011	40.85
2012	44.04
2013	47.65
2014	51.45
2015	55.24
2016	59.07