Year	Percent
1960	12.11029
1961	9.53463
1962	9.9593
1963	11.6259
1964	12.24317
1965	14.90571
1966	16.19606
1967	19.77227
1968	19.07659
1969	21.42851
1970	24.46132
1971	27.83261
1972	26.80015
1973	25.95017
1974	29.49465
1975	33.41298
1976	31.02851
1977	34.78078
1978	34.54536
1979	37.02179
1980	37.32211
1981	43.95887
1982	40.0863
1983	31.57772
1984	30.93193
1985	36.6486
1986	32.6155
1987	30.95061
1988	32.08309
1989	24.80494
1990	26.53888
1991	30.34223
1992	33.5016
1993	32.91742
1994	36.07346
1995	36.4312
1996	30.01898
1997	31.5355
1998	32.50069
1999	40.98182
2000	34.8513
2001	36.92676
2002	31.29638
2003	29.7383
2004	27.5517
2005	26.88452
2006	28.32385
2007	35.21846
2008	33.64328
2009	32.32872
2010	37.20526
2011	34.19397
2012	35.07604
2013	41.30324
2014	44.45255
2015	39.79771
2016	42.60844
2017	48.45413