Year	Percent
1960	36.08457
1961	35.9178
1962	36.44216
1963	35.91255
1964	35.4591
1965	36.78764
1966	39.19919
1967	38.02366
1968	36.9708
1969	37.21722
1970	37.0814
1971	37.41954
1972	38.12201
1973	38.21273
1974	39.96983
1975	41.48629
1976	40.59871
1977	40.67834
1978	41.31981
1979	41.96577
1980	40.91238
1981	41.48837
1982	41.62062
1983	42.95982
1984	44.03242
1985	44.10906
1986	44.43241
1987	44.77562
1988	44.14123
1989	43.62977
1990	43.34997
1991	43.39536
1992	43.25002
1993	44.95023
1994	45.03384
1995	44.86077
1996	45.83499
1997	45.65097
1998	45.29518
1999	45.83816
2000	47.24238
2001	48.3549
2002	49.15107
2003	49.03939
2004	47.31411
2005	48.44853
2006	52.63133
2007	52.76347
2008	53.10654
2009	53.11044
2010	52.83905
2011	50.92806
2012	51.57394
2013	52.00951
2014	51.70125
2015	52.16052
2016	52.77258
2017	53.0924