Year	Number of
1990	20.27
1991	20.58
1992	20.93
1993	21.33
1994	21.74
1995	22.19
1996	22.87
1997	23.59
1998	24.33
1999	25.07
2000	25.87
2001	26.41
2002	27
2003	27.57
2004	28.16
2005	28.81
2006	29.21
2007	29.57
2008	29.98
2009	30.38
2010	30.83
2011	30.73
2012	30.69
2013	30.63
2014	30.61
2015	30.62
2016	30.76