Year	Number of
1990	14.38
1991	14.72
1992	15.41
1993	15.77
1994	15.95
1995	16.02
1996	16.56
1997	17.33
1998	18.43
1999	19.66
2000	21.05
2001	21.59
2002	22.1
2003	23.48
2004	24.62
2005	25.65
2006	26.14
2007	26.81
2008	27.54
2009	28.5
2010	29.56
2011	30.28
2012	31.15
2013	30.89
2014	30.44
2015	30.32
2016	30.5