Year	Percent
1971	25.26165
1972	30.5785
1976	42.74071
1978	52.31364
1979	51.79494
1980	53.39947
1981	50.06323
1982	47.70645
1983	46.68484
1984	40.29306
1985	33.93501
1986	33.70659
1987	32.35234
1988	37.5806
1989	30.372
1990	36.36742
1991	36.38425
1992	37.15054
1994	28.48358
1995	40.44877
1996	46.91687
1999	56.27716
2000	65.24553
2001	72.16607
2003	72.8339
2004	74.80775
2005	74.24746
2006	74.03953
2008	66.59153
2009	65.88428
2010	70.45019
2011	72.04231
2012	75.09017
2013	78.16387
2014	83.86569
2015	82.86474