Year	Number of
1990	13.67
1991	13.81
1992	14.05
1993	14.47
1994	14.28
1995	14.67
1996	13.76
1997	15.24
1998	15.22
1999	15.81
2000	16.81
2001	17.54
2002	18.86
2003	19.04
2004	17.85
2005	18.34
2006	18.11
2007	18.68
2008	19.22
2009	20.86
2010	21.69
2011	22.6
2012	24.56
2013	26.44
2014	26.79
2015	27.43
2016	28.52