Year	Number of
1990	12.51
1991	12.61
1992	12.75
1993	12.96
1994	13.2
1995	13.46
1996	13.76
1997	13.85
1998	13.9
1999	14.03
2000	14.08
2001	14.44
2002	14.87
2003	15.4
2004	16.18
2005	17.45
2006	18.59
2007	19.6
2008	21.86
2009	24.24
2010	26.62
2011	29.38
2012	31.91
2013	34.26
2014	36.67
2015	39.3
2016	41.73