Year	Percent
1987	35.3405
1988	34.29457
1989	32.56238
1990	33.31411
1991	36.68214
1992	36.12646
1993	31.23269
1994	24.25305
1995	24.14345
1996	26.08321
1997	22.87338
1998	22.4
1999	21.0461
2000	20.22996
2001	19.95259
2002	19.38756
2003	20.28618
2004	22.30568
2005	20.7
2006	26.83847
2007	26.86272
2008	29.06507
2009	30.35264
2010	30.31979
2011	30.04246
2012	30.25162
2013	30.51882
2014	30.61214
2015	31.49906
2016	30.08009
2017	30.05426