Year	Percent
1987	54.63
1988	58.1
1989	58.48
1990	56.12
1991	53.17
1992	53.52
1993	49.58
1994	48.56
1995	46.54
1996	44.42
1997	45.09
1998	43.63
1999	40.25
2000	39.8
2001	35.91
2002	37.4
2003	35.18
2004	31.39
2005	30.84
2006	30.5
2007	29.87
2008	31.12
2009	28.5
2010	29
2011	32.05
2012	32.17
2013	22.77
2014	25.31
2015	23.69
2016	22.78