Year	Number of
1990	16.01
1991	16.24
1992	16.33
1993	16.24
1994	16.15
1995	16.29
1996	17.19
1997	18.3
1998	19.93
1999	21.9
2000	24.44
2001	26.05
2002	27.85
2003	29.19
2004	30.76
2005	32.75
2006	32.22
2007	31.91
2008	31.73
2009	31.68
2010	31.67
2011	31.41
2012	31.4
2013	31.49
2014	31.55
2015	31.54
2016	31.61