Year	Number of
1990	20.42
1991	21.08
1992	21.74
1993	22.45
1994	23.2
1995	24.02
1996	24.77
1997	25.57
1998	26.16
1999	26.81
2000	27.77
2001	28.56
2002	29.69
2003	30.55
2004	31.62
2005	32.78
2006	34.1
2007	35.36
2008	36.71
2009	37.94
2010	39.3
2011	40.88
2012	42.34
2013	43.77
2014	45.3
2015	46.95
2016	49.01