Year	Number of
1990	16.5
1991	17.38
1992	18.23
1993	19.23
1994	20.45
1995	21.83
1996	23.17
1997	24.79
1998	25.56
1999	26.1
2000	26.03
2001	26.42
2002	27.63
2003	27.18
2004	28.02
2005	28.8
2006	29.9
2007	31.31
2008	32.37
2009	34.31
2010	35.42
2011	36.68
2012	38.84
2013	40.73
2014	42.73
2015	44.85
2016	46.7