Year	Number of
1990	19.54
1991	19.76
1992	20.22
1993	20.72
1994	21.32
1995	21.56
1996	21.63
1997	21.67
1998	23.02
1999	23.6
2000	25.75
2001	25.47
2002	25.88
2003	27.16
2004	27.16
2005	27.43
2006	27.3
2007	27.72
2008	28.94
2009	29.17
2010	30.03
2011	29.76
2012	30.06
2013	30.45
2014	30.34
2015	30.14
2016	29.88