Year	Percent
1997	24.39578
1999	10.01457
2000	10.54801
2001	10.52031
2002	11.03804
2003	12.5474
2004	11.59984
2005	14.30109
2006	14.91948
2007	15.18528
2008	15.18246
2009	18.25192
2010	19.54295
2011	18.42394
2012	18.32779
2013	19.45244
2014	19.38586
2015	21.29805