Year	Number of
1990	11.23
1991	11.84
1992	12.01
1993	12.02
1994	12.81
1995	13.88
1996	15.68
1997	16.02
1998	17.39
1999	18.1
2000	19.44
2001	20.65
2002	21.28
2003	21.92
2004	22.16
2005	22.38
2006	22.76
2007	23.23
2008	23.79
2009	24.32
2010	24.88
2011	25.37
2012	25.92
2013	26.5
2014	26.9
2015	26.86
2016	27.31