Year	Number of
1990	12.63
1991	12.68
1992	12.82
1993	13.03
1994	13.25
1995	13.46
1996	13.7
1997	13.94
1998	13.86
1999	14.41
2000	14.5
2001	14.72
2002	14.71
2003	15.27
2004	15.71
2005	16.98
2006	17.87
2007	18.72
2008	19.61
2009	19.52
2010	19.56
2011	19.83
2012	20.36
2013	20.92
2014	21.4
2015	21.89
2016	22.52