Year	Number of
1990	13.8
1991	14.67
1992	15.76
1993	16.97
1994	18.55
1995	20.3
1996	22.09
1997	23.92
1998	25.87
1999	27.76
2000	29.83
2001	31.48
2002	33.1
2003	33.96
2004	34.71
2005	35.24
2006	36.2
2007	37.1
2008	38.49
2009	39.58
2010	40.76
2011	41.9
2012	43.36
2013	44.97
2014	46.25
2015	48.08
2016	50.13