Year	Number of
1990	16.6
1991	16.97
1992	17.38
1993	17.83
1994	18.33
1995	18.88
1996	19.38
1997	19.97
1998	20.67
1999	21.29
2000	22.08
2001	22.97
2002	23.91
2003	24.92
2004	25.94
2005	27.02
2006	27.95
2007	28.87
2008	29.81
2009	30.77
2010	31.73
2011	32.45
2012	33.26
2013	34.09
2014	35.03
2015	36.08
2016	37.15