Year	Percent
1960	28.84505
1961	29.3488
1962	29.57522
1963	29.81435
1964	30.08432
1965	30.39049
1966	30.73947
1967	31.1274
1968	31.56027
1969	32.03589
1970	32.56239
1971	33.14051
1972	33.37875
1973	33.44339
1974	33.52489
1975	33.61352
1976	33.70836
1977	33.80777
1978	33.91914
1979	34.04583
1980	34.19249
1981	34.3562
1982	34.27924
1983	34.10635
1984	33.94947
1985	33.80396
1986	33.67232
1987	33.55644
1988	33.46312
1989	33.39627
1990	33.36356
1991	33.14104
1992	32.84915
1993	32.58202
1994	32.33825
1995	32.11468
1996	31.91131
1997	31.72592
1998	31.55871
1999	31.40725
2000	31.27091
2001	31.14714
2002	30.94156
2003	30.70229
2004	30.47799
2005	30.26739
2006	30.07126
2007	29.88884
2008	29.72083
2009	29.5664
2010	29.427
2011	29.30209
2012	29.20061
2013	29.11393
2014	29.03916
2015	28.975
2016	28.92151
2017	28.87739