Year	Number of
1990	12.87
1991	13.48
1992	14.16
1993	14.91
1994	15.72
1995	16.56
1996	17.31
1997	18.09
1998	18.93
1999	19.79
2000	20.69
2001	21.83
2002	23.01
2003	24.24
2004	25.62
2005	27.21
2006	28.64
2007	30.25
2008	32.13
2009	34.15
2010	36.29
2011	38.3
2012	40.43
2013	42.75
2014	45.19
2015	47.76
2016	50.47