Year	Number of
1990	12.29
1991	12.67
1992	13.03
1993	13.42
1994	13.84
1995	14.34
1996	14.77
1997	15.31
1998	15.74
1999	16.32
2000	17.13
2001	17.5
2002	18.09
2003	18.37
2004	18.82
2005	19.46
2006	20.04
2007	20.57
2008	21.04
2009	21.62
2010	22.18
2011	22.69
2012	23.21
2013	23.75
2014	24.33
2015	24.97
2016	25.62