Year	Number of
1990	26.77
1991	27.26
1992	27.82
1993	28.46
1994	29.11
1995	29.78
1996	31.59
1997	33.51
1998	35.56
1999	37.71
2000	40
2001	41.93
2002	43.93
2003	45.97
2004	48.11
2005	50.38
2006	51.7
2007	53
2008	54.35
2009	55.65
2010	56.93
2011	57.03
2012	57.17
2013	57.22
2014	57.35
2015	57.58
2016	58.14