Year	Number of
1990	12.45
1991	12.91
1992	13.46
1993	14.09
1994	14.87
1995	15.8
1996	16.72
1997	17.58
1998	18.15
1999	18.39
2000	18.84
2001	19.47
2002	20.3
2003	21.34
2004	22.4
2005	23.41
2006	24.23
2007	24.95
2008	25.86
2009	26.78
2010	27.81
2011	28.56
2012	26.98
2013	27.66
2014	28.17
2015	28.73
2016	29.34