Year	Number of
1990	16.41
1991	16.67
1992	17.03
1993	17.57
1994	18.13
1995	18.67
1996	19.03
1997	19.37
1998	19.68
1999	20.15
2000	20.42
2001	20.85
2002	21.19
2003	22.29
2004	23.61
2005	24.6
2006	25.28
2007	25.89
2008	26.08
2009	26.9
2010	27.47
2011	28.2
2012	28.8
2013	29.55
2014	30.27
2015	31.02
2016	31.89