Year	Percent
1977	13.02732
1978	16.9898
1979	31.86913
1980	23.16656
1981	26.28714
1982	21.17892
1983	24.52487
1984	24.72338
1985	27.9708
1992	18.68761
1993	17.24357
1994	16.41491
1995	17.02349
1996	14.40152
1997	17.31989
1998	19.23569
1999	12.46407
2000	10.23322
2001	6.85333
2002	9.64981
2003	8.67035
2004	6.43929
2005	5.00835
2006	4.41071
2007	3.30924
2008	2.54583
2009	2.07342
2010	2.67179
2011	3.45402
2012	8.5537
2013	3.65673
2014	4.33075
2015	5.28719