Year	Number of
1990	30.62
1991	30.52
1992	29.96
1993	29.32
1994	29.79
1995	30.46
1996	30.3
1997	30.69
1998	31.51
1999	31.15
2000	30.65
2001	30.93
2002	30.52
2003	29.49
2004	28.93
2005	28.81
2006	29.49
2007	30.51
2008	31.04
2009	31.1
2010	30.89
2011	30.53
2012	30.52
2013	30.6
2014	31.01
2015	31.66
2016	32.59