Year	Number of
1990	10.71
1991	11.17
1992	11.59
1993	11.92
1994	12.14
1995	12.23
1996	12
1997	11.56
1998	11.46
1999	11.62
2000	11.92
2001	12.45
2002	13.38
2003	14.58
2004	15.14
2005	15.06
2006	15.57
2007	16.14
2008	16.98
2009	18.19
2010	19.55
2011	19.89
2012	20.25
2013	20.47
2014	21
2015	21.7
2016	22.29