Year	Percent
1960	27.09401
1961	26.41549
1962	22.33911
1963	20.90483
1964	21.97579
1965	22.49503
1966	24.16397
1967	23.75801
1968	23.85325
1969	25.10573
1970	25.33236
1971	19.35169
1972	16.38097
1973	14.96918
1974	28.55031
1975	40.36975
1976	38.16398
1977	33.8687
1978	36.80653
1979	39.91186
1980	36.16801
1981	31.92419
1982	30.37997
1983	33.9704
1984	36.81483
1985	38.84113
1986	40.37362
1987	43.22545
1988	47.40358
1989	50.94078
1990	48.66236
1991	45.32336
1992	43.92537
1993	41.24324
1994	41.08866
1995	43.46532
1996	45.90748
1997	45.58319
1998	44.3787
1999	44.09781
2000	48.4415
2001	50.29732
2002	50.57731
2003	54.18367
2004	57.76996
2005	60.18144
2006	62.72204
2007	66.31997
2008	70.86318
2009	57.0036
2010	59.63093
2011	61.89554
2012	59.09803
2013	56.08178
2014	56.78548
2015	51.09838
2016	47.76378
2017	48.17024