Year	Number of
1990	31.62
1991	31.87
1992	32.18
1993	32.54
1994	32.92
1995	33.33
1996	34.04
1997	34.8
1998	35.61
1999	36.47
2000	37.42
2001	37.74
2002	38.12
2003	38.56
2004	39.01
2005	39.54
2006	39.46
2007	39.37
2008	39.38
2009	39.45
2010	39.62
2011	39.73
2012	39.94
2013	40.16
2014	40.47
2015	40.86
2016	41.28