Year	Number of
1990	23.91
1991	23.77
1992	23.67
1993	23.69
1994	23.75
1995	23.82
1996	23.91
1997	23.98
1998	24.04
1999	23.86
2000	23.8
2001	23.54
2002	23.51
2003	23.62
2004	23.71
2005	23.57
2006	23.56
2007	22.85
2008	22.46
2009	22.85
2010	24.45
2011	24.58
2012	25.1
2013	26.15
2014	27.28
2015	28.37
2016	29.36