Year	Number of
1990	11.58
1991	12.03
1992	12.49
1993	13
1994	13.53
1995	14.1
1996	15.23
1997	16.45
1998	17.77
1999	19.17
2000	20.66
2001	21.64
2002	22.58
2003	23.47
2004	24.4
2005	25.4
2006	25.8
2007	26.25
2008	26.77
2009	27.32
2010	27.9
2011	28.42
2012	28.97
2013	29.52
2014	30.06
2015	30.57
2016	31.22