Year	Number of
1990	11.42
1991	11.38
1992	11.34
1993	11.21
1994	12.02
1995	13.53
1996	13.72
1997	14.01
1998	14.42
1999	14.63
2000	15.22
2001	15.88
2002	16.86
2003	18.15
2004	18.47
2005	19.5
2006	19.5
2007	20.77
2008	22.25
2009	23.42
2010	24.79
2011	26.59
2012	28.17
2013	30.71
2014	31.13
2015	32.03
2016	33.59