Year	Number of
1990	17.34
1991	17.59
1992	17.83
1993	18.29
1994	18.73
1995	19.12
1996	19.46
1997	19.76
1998	19.68
1999	20.48
2000	20.75
2001	21.21
2002	21.59
2003	22.72
2004	24.13
2005	25.24
2006	26
2007	26.59
2008	26.75
2009	27.59
2010	28.1
2011	28.81
2012	29.48
2013	30.15
2014	30.75
2015	31.39
2016	32.19