Year	Number of
1990	12.6
1991	13.01
1992	13.46
1993	13.94
1994	14.44
1995	14.97
1996	15.64
1997	16.35
1998	17.13
1999	17.92
2000	18.75
2001	18.96
2002	19.18
2003	19.42
2004	19.69
2005	20.05
2006	20.33
2007	20.64
2008	21.02
2009	21.41
2010	21.83
2011	22.63
2012	23.49
2013	24.39
2014	25.34
2015	26.34
2016	27.39