Year	Number of
1990	15.27
1991	15.97
1992	16.67
1993	17.41
1994	18.24
1995	18.87
1996	19.75
1997	21.16
1998	22.31
1999	23.99
2000	24.62
2001	26.08
2002	27.62
2003	29.15
2004	30.65
2005	32.27
2006	34
2007	36.03
2008	37.75
2009	39.4
2010	40.71
2011	42.14
2012	43.52
2013	45.05
2014	46.68
2015	48.48
2016	49.73