Year	Number of
1990	11.66
1991	12.21
1992	12.55
1993	12.88
1994	13.23
1995	13.57
1996	13.7
1997	13.74
1998	13.86
1999	14.34
2000	14.57
2001	14.56
2002	14.59
2003	14.66
2004	14.71
2005	14.87
2006	14.88
2007	15.06
2008	15.17
2009	15.37
2010	15.7
2011	16.06
2012	16.41
2013	16.74
2014	17.09
2015	17.45
2016	17.74