Year	Number of
1990	23.9
1991	22.65
1992	23.23
1993	24.65
1994	25.44
1995	25.81
1996	26.46
1997	27.63
1998	29.24
1999	30.96
2000	32.57
2001	33.88
2002	34.98
2003	36.36
2004	36.64
2005	36.49
2006	37.68
2007	38.38
2008	39.22
2009	39.31
2010	39.92
2011	40.58
2012	41.15
2013	41.4
2014	42.24
2015	42.69
2016	43.02