Year	Percent
1977	12.51052
1978	11.3407
1979	12.82681
1980	18.28803
1981	18.84332
1982	21.46613
1983	20.33126
1984	16.34903
1985	19.17094
1986	18.42265
1987	18.79514
1989	31.49967
1990	29.41472
1991	29.3569
1992	27.86137
1993	23.33959
1994	25.86069
1995	27.655
1996	30.49377
1997	29.0571
1998	32.09029
1999	28.72771
2000	30.13569
2001	26.83993
2002	24.17927
2003	24.24553
2004	23.16436
2005	27.30933
2006	33.48988
2007	30.48499
2008	29.42903
2009	28.02456
2010	27.95629
2011	30.14265
2012	31.3185
2013	28.69698
2014	32.15117
2015	24.69408
2016	24.69507
2017	27.02329