Year	Percent
1997	7.93639
1999	18.14052
2000	15.85101
2001	16.3786
2002	18.26466
2003	17.10819
2004	16.50568
2005	14.92814
2006	14.46808
2007	14.3347
2008	14.65799
2009	17.8898
2010	17.79922
2011	17.26915
2012	17.85945
2013	18.48036
2014	19.06034
2015	19.09876