Year	Number of
1990	12.36
1991	12.43
1992	12.66
1993	12.94
1994	13.27
1995	13.61
1996	13.87
1997	14.16
1998	14.39
1999	14.7
2000	14.8
2001	15.02
2002	15
2003	15.58
2004	16
2005	17.27
2006	18.16
2007	19.1
2008	20.1
2009	20.05
2010	20.22
2011	20.59
2012	21.17
2013	21.9
2014	22.59
2015	23.27
2016	24.07