Year	Percent
1960	36.32479
1961	33.98457
1962	44.15861
1963	40.17361
1964	43.76063
1965	42.5201
1966	41.73113
1967	43.96098
1968	41.6569
1969	41.42033
1970	41.47184
1971	41.91543
1972	41.37057
1973	40.82077
1974	40.86263
1975	42.14069
1976	41.64866
1977	41.13238
1978	42.70802
1979	43.4481
1980	40.79929
1981	40.88125
1982	40.85766
1983	40.52528
1984	39.04094
1985	39.26908
1986	38.87781
1987	39.69979
1988	41.78991
1989	48.36731
1990	45.15165
1991	48.84633
1992	47.05569
1993	44.13046
1994	43.4584
1995	58.12142
1996	60.31888
1997	60.60571
1998	61.11859
1999	60.20366
2000	58.25186
2001	57.71369
2002	57.34815
2003	56.35783
2004	54.92047
2005	56.07589
2006	57.13813
2007	57.72624
2008	56.80486
2009	59.14506
2010	57.61292
2011	57.56817
2012	58.7336
2013	59.67876
2014	61.25097
2015	62.30812
2016	63.23042
2017	63.06615