Year	Number of
1990	15.58
1991	15.45
1992	15.33
1993	15.37
1994	15.44
1995	15.5
1996	16.16
1997	16.37
1998	16.89
1999	17.49
2000	18.25
2001	18.18
2002	18.09
2003	18.49
2004	18.55
2005	19.12
2006	20.08
2007	20.64
2008	21.3
2009	22.52
2010	23.03
2011	23.4
2012	24.06
2013	24.92
2014	26.75
2015	28.18
2016	29.89