Year	Number of
1990	19.67
1991	20.22
1992	20.89
1993	21.49
1994	22.13
1995	22.81
1996	23.37
1997	23.99
1998	24.66
1999	25.32
2000	26.12
2001	25.73
2002	26.24
2003	26.77
2004	27.39
2005	28.13
2006	28.76
2007	28.67
2008	28.59
2009	28.47
2010	29.22
2011	29.86
2012	30.46
2013	31.08
2014	31.7
2015	32.29
2016	32.86