Year	Number of
1990	10.65
1991	10.63
1992	10.53
1993	10.34
1994	10.17
1995	9.99
1996	9.74
1997	9.94
1998	10.17
1999	10.06
2000	10.52
2001	10.89
2002	11.39
2003	12.13
2004	12.72
2005	13.51
2006	14.07
2007	14.72
2008	15.31
2009	16.13
2010	16.83
2011	17.61
2012	18.47
2013	19.43
2014	20.38
2015	21.31
2016	22.26