Year	Percent
1987	29.93397
1988	30.02813
1989	27.85058
1990	28.54066
1991	28.87724
1992	29.4344
1993	40.40318
1994	32.51222
1995	37.47605
1996	42.42201
1997	43.83227
1998	42.07304
1999	39.25883
2000	39.52902
2001	43.24991
2002	45.3018
2003	47.90233
2004	47.34536
2005	50.42428
2006	48.09456
2007	49.14649
2008	50.83782
2009	54.17854
2010	55.08465
2011	53.04537
2012	54.00183
2013	56.26557
2014	54.15892
2015	51.10805
2016	50.16075
2017	50.26756