Year	Number of
1990	12.75
1991	12.28
1992	11.95
1993	11.82
1994	12.17
1995	13.13
1996	13.42
1997	13.6
1998	14.01
1999	12.97
2000	12.73
2001	12.62
2002	12.93
2003	12.97
2004	12.61
2005	12.8
2006	12.47
2007	12.64
2008	12.84
2009	13.25
2010	13.63
2011	14.32
2012	14.84
2013	15.73
2014	16.42
2015	17.05
2016	17.99