Year	Percent
1987	39.57
1988	42.57
1989	42.72
1990	40.57
1991	37.84
1992	38.37
1993	34.31
1994	33.99
1995	31.23
1996	28.94
1997	30.33
1998	29.77
1999	27.12
2000	26.93
2001	24.69
2002	25.57
2003	24.6
2004	22.16
2005	21.56
2006	21.52
2007	21.36
2008	22.25
2009	20.39
2010	20.95
2011	23.56
2012	23.98
2013	16.91
2014	17.93
2015	17.06
2016	16.57