Year	Percent
1977	4.39946
1978	6.51671
1979	7.74317
1980	8.32841
1981	9.36123
1982	11.90055
1983	16.3551
1984	22.53164
1985	29.03156
1986	33.37043
1987	31.54622
1988	29.22157
1989	21.43264
1990	15.42533
1991	18.5576
1992	27.26973
1993	16.01252
1994	14.15797
1995	12.76676
1996	13.67765
1997	11.35504
1998	10.23378
1999	10.84281
2000	9.72174
2001	10.06451
2002	10.28397
2003	10.74596
2004	14.46445
2005	14.77139
2006	15.83868
2007	16.36485
2008	15.29561
2009	18.02693
2010	14.36569
2011	15.65325
2012	12.24888
2013	22.17767
2014	13.68852
2015	14.88071
2016	22.25349