Year	Percent
1960	38.95329
1961	39.71419
1962	40.11404
1963	41.13269
1964	44.13483
1965	44.4543
1966	44.67409
1967	46.35886
1968	48.13998
1969	51.00311
1970	49.63958
1971	49.42687
1972	50.46128
1973	51.2073
1974	58.44384
1975	54.7154
1976	59.1562
1977	60.57692
1978	57.63967
1979	56.53761
1980	54.37927
1981	54.87793
1982	54.58658
1983	56.6375
1984	56.31724
1985	53.71635
1986	50.25603
1987	48.4528
1988	45.30985
1989	45.49986
1990	41.23436
1991	42.10759
1992	41.54831
1993	49.0309
1994	53.69655
1995	54.50439
1996	54.97903
1997	53.03054
1998	53.04523
1999	54.8906
2000	53.5064
2001	52.79676
2002	51.62606
2003	50.14562
2004	54.39967
2005	54.58991
2006	53.84263
2007	54.73348
2008	52.9319
2009	53.75322
2010	53.0623
2011	42.57499
2012	42.66058
2013	42.86735
2014	41.08363
2015	40.60816
2016	40.8547
2017	41.58367