Year	Percent
1997	15.74331
1998	14.37161
1999	14.55747
2000	13.21789
2001	12.89313
2006	16.21294
2007	16.38479
2008	15.35419
2009	14.79187
2011	12.38945
2012	13.26958
2013	13.19767
2014	12.57708
2015	13.41453