Year	Percent
1970	21.99292
1971	22.25366
1972	24.29377
1975	28.19639
1976	29.28851
1977	29.14379
1978	30.2188
1979	30.66298
1980	32.53762
1981	32.65407
1982	32.63379
1983	33.86895
1984	35.27242
1985	36.71995
1986	39.5741
1996	45.51718
1999	50.78722
2000	55.51237
2001	58.03934
2002	61.58016
2004	67.26301
2005	70.9242
2006	73.92884
2007	74.67074
2008	77.55839
2009	81.62691
2010	83.62597
2011	85.79196
2012	84.75145
2013	84.86241
2014	84.66885
2015	82.71167