Year	Number of
1990	19.54
1991	19.73
1992	19.75
1993	19.61
1994	19.58
1995	19.82
1996	19.9
1997	20.4
1998	20.97
1999	21.8
2000	22.12
2001	22.26
2002	22.57
2003	22.95
2004	23.54
2005	23.17
2006	22.74
2007	22.49
2008	22.32
2009	22.63
2010	23.21
2011	22.93
2012	22.92
2013	23.74
2014	24.72
2015	25.64
2016	26.62