Year	Number of
1990	13.17
1991	13.32
1992	13.46
1993	13.63
1994	13.83
1995	13.93
1996	14.15
1997	14.62
1998	14.98
1999	15.44
2000	15.6
2001	16.26
2002	16.95
2003	17.7
2004	18.43
2005	19.18
2006	19.94
2007	20.78
2008	21.45
2009	22.13
2010	22.61
2011	22.84
2012	23.09
2013	23.37
2014	23.7
2015	24.1
2016	24.48