Year	Number of
1990	17.43
1991	17.95
1992	18.4
1993	18.19
1994	18.86
1995	19.12
1996	17.97
1997	17.15
1998	16.65
1999	15.75
2000	16.07
2001	15.48
2002	15.58
2003	15.83
2004	15.96
2005	15.5
2006	15.45
2007	14.92
2008	15.07
2009	15.21
2010	15.19
2011	15.12
2012	15.22
2013	15.5
2014	15.63
2015	15.77
2016	15.06