Year	Percent
1971	21.06888
1972	23.05335
1976	34.50249
1977	38.14415
1978	41.64811
1980	43.12843
1981	46.38871
1982	48.26494
1983	51.93892
1984	55.73688
1988	36.61116
1991	38.957
1992	36.19987
1993	45.25206
1994	37.15902
1999	32.26506
2002	34.3161
2007	44.81166
2008	49.72137
2009	51.82725
2010	54.77845
2011	54.9794
2012	60.64633
2013	62.72308
2015	70.37636