Year	Percent
1960	29.55091
1961	29.32397
1962	29.40692
1963	28.61388
1964	27.4359
1965	25.70405
1966	25.28045
1967	24.57067
1968	25.24673
1969	23.00184
1970	21.19945
1971	21.27484
1972	24.6315
1973	24.62371
1974	27.16114
1975	26.84311
1976	26.88429
1977	29.30776
1978	31.38548
1979	34.16634
1980	34.34115
1981	27.47056
1982	25.61859
1983	23.95626
1984	24.688
1985	30.44215
1986	29.60159
1987	29.30869
1988	28.18824
1989	25.86726
1990	23.49492
1991	21.09804
1992	20.70374
1993	21.82513
1994	21.47419
1995	22.1356
1996	24.08026
1997	23.98733
1998	25.00505
1999	24.69521
2000	27.15888
2001	29.37483
2002	31.78084
2003	26.88506
2004	25.4671
2005	26.44666
2006	29.27389
2007	31.17385
2008	35.62244
2009	27.91189
2010	28.61524
2011	30.46094
2012	29.72388
2013	30.97134
2014	31.46865
2015	30.15605
2016	30.7026
2017	29.77289