Year	Number of
1990	11.66
1991	11.89
1992	12.26
1993	12.77
1994	13.29
1995	13.78
1996	14.37
1997	14.88
1998	15.39
1999	15.96
2000	16.63
2001	17.44
2002	18.39
2003	19.35
2004	20.33
2005	21.32
2006	22.21
2007	23.11
2008	24.03
2009	25.07
2010	26.25
2011	27.05
2012	27.96
2013	28.83
2014	29.72
2015	30.62
2016	31.66