Year	Number of
1990	12.64
1991	12.91
1992	13.22
1993	13.58
1994	13.99
1995	14.39
1996	14.91
1997	15.2
1998	15.48
1999	15.86
2000	16.11
2001	16.54
2002	17.01
2003	17.35
2004	18.06
2005	19.41
2006	20.26
2007	23.38
2008	25.73
2009	28.17
2010	30.6
2011	33.49
2012	36.07
2013	38.43
2014	40.81
2015	43.38
2016	45.81