Year	Number of
1990	12.16
1991	12.45
1992	12.78
1993	13.15
1994	13.54
1995	13.85
1996	14.18
1997	14.52
1998	14.54
1999	15.34
2000	15.77
2001	16.29
2002	16.7
2003	17.55
2004	19.33
2005	20.87
2006	22.12
2007	23.26
2008	23.98
2009	25.36
2010	26.2
2011	27.4
2012	29
2013	29.94
2014	30.92
2015	31.92
2016	33.1