Year	Number of
1990	10.79
1991	10.96
1992	11.14
1993	11.38
1994	11.72
1995	12.3
1996	12.48
1997	13.12
1998	13.61
1999	14.38
2000	15.18
2001	15.31
2002	15.44
2003	15.56
2004	15.27
2005	14.85
2006	14.66
2007	14.3
2008	14.13
2009	14.31
2010	13.75
2011	13.48
2012	13.59
2013	13.68
2014	13.9
2015	14.12
2016	14.26