Year	Number of
1990	17.96
1991	18.62
1992	19.31
1993	20.03
1994	20.8
1995	21.64
1996	22.32
1997	23.08
1998	23.89
1999	24.78
2000	25.76
2001	26.58
2002	27.46
2003	28.33
2004	29.3
2005	30.4
2006	32.07
2007	33.84
2008	35.71
2009	37.58
2010	39.43
2011	40.69
2012	42
2013	43.28
2014	44.6
2015	45.97
2016	47.33