Year	Percent
1970	33.49027
1971	33.11143
1972	33.85413
1973	27.70015
1974	24.07968
1975	28.2408
1976	35.85474
1977	41.951
1978	47.72746
1979	48.6877
1980	54.40913
1981	59.18641
1982	67.63223
1983	74.83376
1984	81.36941
1985	90.54972
1986	98.79784
1987	93.15033
1988	78.8913
1989	69.73498
1990	70.18943
1991	71.87272
1992	62.01938
1993	65.36627
1994	61.05545
1995	51.50911
1996	51.08687
1997	58.26565
1998	64.89633
1999	61.91646
2000	61.55252
2001	64.82322
2002	62.25029
2003	61.06594
2004	54.34891
2005	45.21644
2006	37.49259
2007	31.62863
2008	26.41838
2009	25.05811
2010	24.57704
2011	24.62403
2012	23.01743
2013	20.04442
2014	22.77863
2015	22.76549
2016	21.06709