Year	Number of
1990	13.24
1991	13.34
1992	13.49
1993	13.66
1994	13.87
1995	14.11
1996	14.39
1997	14.71
1998	15.09
1999	15.53
2000	16.06
2001	16.16
2002	16.35
2003	16.62
2004	16.96
2005	17.37
2006	17.9
2007	18.47
2008	19.1
2009	19.77
2010	20.49
2011	21.73
2012	23.11
2013	24.63
2014	26.29
2015	28.09
2016	30.21