Year	Number of
1990	10.22
1991	10.42
1992	10.59
1993	10.76
1994	10.91
1995	11.04
1996	11.22
1997	11.38
1998	11.56
1999	11.87
2000	12.09
2001	12.13
2002	12.2
2003	12.28
2004	12.29
2005	12.17
2006	12.79
2007	13.69
2008	14.42
2009	15.89
2010	16.61
2011	17.07
2012	17.88
2013	18.98
2014	20.18
2015	21.42
2016	22.62