Year	Number of
1990	14.36
1991	14.51
1992	15.32
1993	15.85
1994	16.51
1995	16.73
1996	17.15
1997	17.97
1998	18.54
1999	19.05
2000	19.44
2001	19.59
2002	20.3
2003	20.87
2004	21.27
2005	21.84
2006	22.14
2007	22.88
2008	23.71
2009	24.38
2010	25.34
2011	25.96
2012	26.48
2013	27.67
2014	29.08
2015	29.71
2016	30.36