Year	Number of
1990	15.06
1991	15.23
1992	15.61
1993	16.05
1994	16.48
1995	16.86
1996	16.45
1997	15.94
1998	15.46
1999	14.96
2000	14.47
2001	14.35
2002	14.23
2003	14.1
2004	14
2005	13.93
2006	13.9
2007	13.89
2008	13.9
2009	13.94
2010	14.01
2011	14.39
2012	14.75
2013	15.11
2014	15.47
2015	15.86
2016	16.23