Year	Number of
1990	13.41
1991	14.03
1992	14.68
1993	15.34
1994	15.93
1995	16.41
1996	16.47
1997	16.35
1998	16.13
1999	15.96
2000	15.93
2001	16.01
2002	16.35
2003	16.87
2004	17.37
2005	17.79
2006	18.88
2007	19.91
2008	21.01
2009	22.13
2010	23.31
2011	24.27
2012	25.19
2013	26.01
2014	26.93
2015	27.96
2016	28.84