Year	Number of
1990	13.91
1991	14.35
1992	14.77
1993	15.2
1994	15.66
1995	16.17
1996	16.53
1997	16.96
1998	17.45
1999	17.95
2000	18.45
2001	18.81
2002	19.18
2003	19.6
2004	20.04
2005	20.51
2006	20.98
2007	21.45
2008	21.93
2009	22.44
2010	22.96
2011	23.62
2012	24.3
2013	24.97
2014	25.65
2015	26.37
2016	27.16