Year	Percent
1996	19.37
1997	22.04
1998	23.66
1999	23.02
2000	22.31
2001	22.12
2002	23.26
2003	23.91
2004	24.75
2006	28.15
2007	30.32
2009	30.59
2010	29.45
2011	30.41
2012	31.43
2013	32
2014	32.2
2015	33.24
2016	33.37
2017	34.07